Pore Initiation Technique

ABSTRACT

A technique for initiating the formation of pores in a polymeric material that contains a thermoplastic composition is provided. The thermoplastic composition contains microinclusion and nanoinclusion additives dispersed within a continuous phase that includes a matrix polymer. To initiate pore formation, the polymeric material is mechanically drawn (e.g., bending, stretching, twisting, etc.) to impart energy to the interface of the continuous phase and inclusion additives, which enables the inclusion additives to separate from the interface to create the porous network. The material is also drawn in a solid state in the sense that it is kept at a temperature below the melting temperature of the matrix polymer.

The present application claims priority to U.S. provisional applicationsSer. Nos. 61/833 989, filed on Jun. 12, 2013, and 61/907,556, filed onNov. 22, 2013, which are incorporated herein in their entirety byreference thereto.

BACKGROUND OF THE INVENTION

Significant efforts have been made to produce low density polymericmaterials to improve the use of natural resources and reduction of thecarbon footprint in finished products. A typical approach to producingsuch low density materials is by foaming the polymer using physical orchemical blowing agents, which create gas-filled pores though the bulk.Chemical blowing agents are compounds that undergo chemical reactionliberating gas that creates the pore structure through the bulk of thepolymer. Physical blowing agents are typically compressed gases that aredispersed in the polymer and expand creating the pores. Regardless,typical foaming processes induce low molecular orientation because thepore formation happens when the polymer is in the molten state. Thisreduces the melt strength, thus leading to breaks in high speedproduction processes with high deformation rates (e.g., fiber spinning,film formation, molding, etc.).

As such, a need currently exists for an improved technique for creatingpores in polymeric materials.

SUMMARY OF THE INVENTION

In accordance with one embodiment of the present invention, a method orinitiating the formation of pores in a polymeric material that contain athermoplastic composition is disclosed. The thermoplastic compositionincludes a continuous phase in which a microinclusion additive andnanoinclusion additive are dispersed in the form of discrete domains,the continuous phase including a matrix polymer. The method comprisesmechanically drawing the polymeric material in a solid state to form aporous network, wherein the porous network includes a plurality ofnanopores having an average cross-sectional dimension of about 800nanometers or less.

Other features and aspects of the present invention are discussed ingreater detail below.

DESCRIPTION OF THE DRAWINGS

A full and enabling disclosure of the present invention, including thebest mode thereof, directed to one of ordinary skill in the art, is setforth more particularly in the remainder of the specification whichmakes reference to the appended figures in which:

FIG. 1 is a perspective view of grooved rolls that may be used tomechanically draw a polymeric material in accordance with one embodimentof the present invention;

FIG. 2 is a cross-sectional view showing the engagement between two ofthe grooved rolls of FIG. 1;

FIGS. 3-4 are SEM microphotographs of the unstretched film of Example 7(film was cut parallel to machine direction orientation);

FIGS. 5-6 are SEM microphotographs of the stretched film of Example 7was cut parallel to machine direction orientation);

FIGS. 7-8 are SEM microphotographs of the unstretched film of Example 8,where the film was cut perpendicular to the machine direction in FIG. 7and parallel to the machine direction in FIG. 8;

FIGS. 9-10 are SEM microphotographs of the stretched film of Example 8(film was cut parallel to machine direction orientation);

FIG. 11 is an SEM photomicrograph (1,000×) of the fiber of Example 9(polypropylene, polylactic acid, and polyepoxide) after freezefracturing in liquid nitrogen;

FIG. 12 is an SEM photomicrograph (5,000×) of the fiber of Example 9(polypropylene, polylactic acid, and polyepoxide) after freezefracturing in liquid nitrogen; and

FIG. 13 is an SEM photomicrograph (10,000×) of the fiber surface ofExample 9 (polypropylene, polylactic acid, and polyepoxide).

Repeat use of references characters in the present specification anddrawings is intended to represent same, or analogous features orelements of the invention.

DETAILED DESCRIPTION OF REPRESENTATIVE EMBODIMENTS

Reference now will be made in detail to various embodiments of theinvention, one or more examples of which are set forth below. Eachexample is provided by way of explanation of the invention, notlimitation of the invention. In fact, it will be apparent to thoseskilled in the art that various modifications and variations may be madein the present invention without departing from the scope or spirit ofthe invention. For instance, features illustrated or described as partof one embodiment, may be used on another embodiment to yield a stillfurther embodiment. Thus, it is intended that the present inventioncovers such modifications and variations as come within the scope of theappended claims and their equivalents.

Generally speaking, the present invention is directed to a technique forinitiating the formation of pores in a polymeric material that containsa thermoplastic composition. The thermoplastic composition containsmicroinclusion and nanoinclusion additives dispersed within a continuousphase that includes a matrix polymer. To initiate pore formation, thepolymeric material is mechanically drawn (e.g., bending, stretching,twisting, etc.) to impart energy to the interface of the continuousphase and inclusion additives, which enables the inclusion additives toseparate from the interface to create the porous network. The materialis also drawn in a solid state in the sense that it is kept at atemperature (“drawing temperature”) below the melting temperature of thematrix polymer. Among other things, this helps to ensure that thepolymer chains are not altered to such an extent that the porous networkbecomes unstable. For example, the material may be drawn at atemperature of from about −50° C. to about 125° C., in some embodimentsfrom about −25° C. to about 100° C., and in some embodiments, from about−20° C. to about 50° C. The drawing temperature may also be below theglass transition temperature of the component having the highest glasstransition temperature (e.g., matrix polymer, microinclusion additiveetc.). For example, the drawing temperature may be at least about 10°C., in some embodiments at least about 20° C., and in some embodimentsat least about 30° C. below the glass transition temperature of thematrix polymer and/or microinclusion additive.

The microinclusion and nanoinclusion additives may also be selected sothat they are at least partially incompatible with the matrix polymer sothat they become dispersed within the continuous phase as discretemicro-scale and nano-scale phase domains respectively. Thus, duringmechanical drawing when the composition is subjected to a deformationand elongational strain, these micro-scale and nano-scale phase domainsare able to interact in a unique manner to create a network of pores, asubstantial portion of which are of a nano-scale size. Namely, it isbelieved that elongational strain can initiate intensive localized shearzones and/or stress intensity zones (e.g., normal stresses) near themicro-scale discrete phase domains as a result of stress concentrationsthat arise from the incompatibility of the materials. These shear and/orstress intensity zones cause some initial debonding in the polymermatrix adjacent to the micro-scale domains. Notably, however, localizedshear and/or stress intensity zones may also be created near thenano-scale discrete phase domains that overlap with the micro-scalezones. Such overlapping shear and/or stress intensity zones cause evenfurther debonding to occur in the polymer matrix, thereby creating asubstantial number of nanopores adjacent to the nano-scale domainsand/or micro-scale domains. In addition, because the pores are locatedadjacent to the discrete domains, a bridge can be formed between theboundaries of the pores that act as internal structural “hinges” thathelp stabilize the network and increase its ability to dissipate energy.

Through the techniques noted above, a unique porous network may beformed in the polymeric material so that the average percent volumeoccupied by the pores within a given unit volume of the material may befrom about 15% to about 80% per cm³, n some embodiments from about 20%to about 70%, and in some embodiments, from about 30% to about 60% percubic centimeter of the material. With such a pore volume, the materialmay have a relatively low density, such as about 1.2 grams per cubiccentimeter (“g/cm³”) or less in some embodiments about 1.0 g/cm³ orless, in some embodiments from about 0.2 g/cm³ to about 0.8 g/cm³, andin some embodiments, from about 0.1 g/cm³ to about 0.5 g/cm³. Asubstantial portion of pores in the porous network are also of a“nano-scale” size (“nanopores”), such as those having an averagecross-sectional dimension of about 800 nanometers or less, in someembodiments from about 5 to about 700 nanometers, and n someembodiments, from about 10 to about 500 nanometers. The term“cross-sectional dimension” generally refers to a characteristicdimension (e.g., width or diameter) of a pore, which is substantiallyorthogonal to its major axis (e.g., length) and also typicallysubstantially orthogonal to the direction of the stress applied duringdrawing. Such nanopores may, for example, constitute to about 15 vol. %or more, in some embodiments about 20 vol. % or more in some embodimentsfrom about 30 vol. % to 100 vol. %, and in some embodiments, from about40 vol. % to about 90 vol. % of the total pore volume in the polymericmaterial.

Besides a reduced density, the nanoporous structure may also provide avariety of functional benefits to the resulting polymeric material. Forexample, such a structure can help restrict the flow of fluids throughthe material and be generally impermeable to fluids (e.g., liquidwater), thereby a lowing the material to insulate a surface from waterpenetration. In this regard, the polymeric material may have arelatively high hydrohead value of about 50 centimeters (“cm”) or more,in some embodiments about 100 cm or more, in some embodiments, about 150cm or more, and in some embodiments, from about 200 cm to about 1000 cm,as determined in accordance with ATTCC 127-2008. Other beneficialproperties may also be achieved. For example, the resulting polymericmaterial may be generally permeable to water vapors. The permeability ofthe material to water vapor may characterized by its relatively highwater vapor transmission rate (“WVTR”), which is the rate at which watervapor permeates through a material as measured in units of grams permeter squared per 24 hours (g/m²/24 hrs). For example, the polymericmaterial may exhibit a WVTR of about 300 g/m²-24 hours or more in someembodiments about 500 g/m²-24 hours or more, in some embodiments about1,000 g/m²-24 hours or more, and in some embodiments, from about 3,000to about 15,000 g/m²-24 hours, such as determined in accordance withASTM E96/96M-12, Procedure B or INDA Test Procedure IST-70.4 (01). Thepolymeric material can also act as a thermal barrier that exhibits arelatively low thermal conductivity, such as about 0.40 watts permeter-kelvin (“W/m-K”) or less, in some embodiments about 0.20 W/m-K orless, in some embodiments about 0.15 W/m-K or less, in some embodimentsfrom about 0.01 to about 0.12 W/m-K, and in some embodiments, from about0.02 to about 0.10 W/m-K. Notably, the material is capable of achievingsuch low thermal conductivity values at relatively low thicknesses,which can allow the material to possess a greater degree of flexibilityand conformability, as well as reduce the space it occupies in anarticle. For this reason, the polymeric material may also exhibit arelatively low “thermal admittance”, which is equal to the thermalconductivity of the material divided by its thickness and is provided inunits of watts per square meter-kelvins (“W/m²K”). For example, thematerial may exhibit a thermal admittance of about 1000 W/m²K or less,in some embodiments from about 10 to about 800 W/m²k, in someembodiments from about 20 to about 500 W/m²K, and in some embodiments,fro about 40 to about 200 W/m²K. The actual thickness of the polymericmaterial may depend on its particular form, but typically ranges fromabout 5 micrometers to about 100 millimeters, in some embodiments fromabout 10 micrometers to about 50 millimeters, in some embodiments fromabout 200 micrometers to>>about 25 millimeters.

Various embodiments of the present invention will now be described inmore detail.

I. Thermoplastic Composition

A. Matrix Polymer

As indicated above, the thermoplastic composition contains a continuousphase within which the microinclusion and nanoinclusion additives aredispersed The continuous phase contains one or more matrix polymers,which typically constitute from about 60 wt. % to about 99 wt. % in someembodiments from about 75 wt. % to about 98 wt. %, and in someembodiments, from about 80 wt. % to about 95 wt. % of the thermoplasticcomposition. The nature of the matrix polymer(s) used to form thecontinuous phase is not critical and any suitable polymer may generallybe employed, such as polyesters, polyolefins, styrenic polymers,polyamides, etc. In certain embodiments, for example, polyesters may beemployed in the composition to form the polymer matrix. Any of a varietyof polyesters may generally be employed, such as aliphatic polyesters,such as polycaprolactone, polyesteramides, polylactic acid (PLA) and itscopolymers, polyglycolic acid, polyalkylene carbonates (e.g.,polyethylene carbonate), poly-3-hydroxybutyrate (PHB)poly-3-hydroxyvalerate (PHV),poly-3-hydroxybutyrate-co-4-hydroybutyrate,poly-3-hydroxybutyrate-co-3-hydroxyvalerate copolymers (PHBV),poly-3-hydroxylbutyrate-co-3-hydroxyhexanoate,poly-3-hydroxybutyrate-co-3-hydroxyoctanoate,poly-3-hydroxybutyrate-co-3-hydroxydecanoate,poly-3-hydroxybutyrate-co-3-hydroxyoctadecanoate, and succinate-basedaliphatic polymers (e.g., polybutylene succinate, polybutylene succinateadipate, polyethylene succinate, etc.); aliphatic-aromatic copolyesters(e.g., polybutylene adipate terephthalate, polyethylene adipateterephthalate polyethylene adipate isophthalate, polybutylene adipateisophthalate etc.); aromatic polyesters (e.g., polyethyleneterephthalate, polybutylene terephthalate, etc.); and so forth.

In certain cases, the thermoplastic composition may contain at least onepolyester that is rigid in nature and thus has a relatively high glasstransition temperature. For example, the glass transition temperature(“T_(g)”) may be about 0° C. or more, in some embodiments from about 5°C. to about 100° C., in some embodiments from about 30° C. to about 80°C., and in some embodiments, from about 50° C. to about 75° C. Thepolyester may also have a melting temperature of from about 140° C. toabout 300° C., in some embodiments from about 150° C. to about 250° C.,and in some embodiments, from about 160° C. to about 220° C. Theernperature may be determined using, differential scanning calorimetry(“DSC”) in accordance with ASTM D-3417. The glass transition temperaturemay be determined by dynamic mechanical analysis in accordance with ASTME1640-09.

One particularly suitable rigid polyester is polylactic acid, which maygenerally be derived from monomer units of any isomer of lactic acid,such as levorotory-lactic acid (“L-lactic acid”) dextrorotatory-lacticacid (“D-lactic acid”), meso-lactic acid or mixtures thereof. Monomerunits may also be formed from anhydrides of any isomer of lactic acid,including L-lactide, D-lactide meso-lactide, or mixtures thereof. Cyclicdimers of such lactic acids and/or lactides may also be employed. Anyknown polymerization method, such as polycondensation or ring-openingpolymerization, may be used to polymerize lactic acid. A small amount ofa chain-extending agent (e.g., a diisocyanate compound, an epoxycompound or an acid anhydride) may also be employed. The polylactic acidmay be a homopolymer or a copolymer, such as one that contains monomerunits derived from L-lactic acid and monomer units derived from D-lacticacid. Although not required, the rate of content of one of the monomerunit derived from L-lactic acid and the monomer unit derived fromD-lactic acid is preferably about 85 mole % or more, in some embodimentsabout 90 mole % or more, and in some embodiments, about 95 mole % ormore. Multiple polylactic acids, each having a different ratio betweenthe monomer unit derived from L-lactic acid and the monomer unit derivedfrom D-lactic acid, may be blended at an arbitrary percentage. Ofcourse, polylactic acid may also be ended with other types of polymers(e.g., polyolefins, polyesters, etc.).

In one particular embodiment the polylactic acid has the followinggeneral structure:

One specific example of a suitable polylactic acid polymer that may beused in the present invention is commercially available from Biomer,Inc. of Krailling, Germany) under the name BIOMER™ L9000. Other suitablepolylactic acid polymers are commercially available from Natureworks LCof Minnetonka, Minn. (NATUREWORKS®) or Mitsui Chemical (LACEA™). Stillother suitable polyactic acids may be described in U.S. Pat. Nos.4,797,468; 5,470,944; 5,770,682; 5,821,327; 5,880,254; and 6,326,458.

The polylactic acid typically has a number average molecular weight(“M_(n)”) ranging from about 40,000 to about 180,000 grams per mole, insome embodiments from about 50,000 to about 160,000 grams per mole, andin some embodiments, from about 80,000 to about 120,000 grams per mole.Likewise the polymer also typically has a weight average molecularweight (“M_(w)”) ranging from about 80,000 to about 250,000 grams permole, in some embodiments from about 100,000 to about 200,000 grams permole, and in some embodiments, from about 110,000 to about 160,000 gramsper mole. The ratio of the weight average molecular weight to the numberaverage molecular weight (“M_(w)/M_(n)”) i.e., the “polydispersityindex”, is also relatively low. For example, the polydispersity indextypically ranges from about 1.0 to about 3.0, in some embodiments fromabout 1.1 to about 2.0, and in some embodiments, from about 1.2 to about1.8. The weight and number average molecular weights may be determinedby methods known to those skilled in the art.

The polylactic acid may also have an apparent viscosity of from about 50to about 600 Pascal seconds (Pa·s), in some embodiments from about 100to about 500 Pa·s, and n some embodiments, from about 200 to about 400Pa·s, as determined at a temperature of 190° C. and a shear rate of 1000sec⁻¹. The melt flow rate of the polylactic acid (on a dry basis) mayalso range from about 0.1 to about 40 grams per 10 minutes, in someembodiments from about 0.5 to about 20 grams per 10 minutes, and in someembodiments, from about 5 to about 15 grams per 10 minutes, determinedat a load of 2160 grams and at 190° C.

Some types of neat polyesters (e.g., polylactic acid) can absorb waterfrom the ambient environment such that it has a moisture content ofabout 500 to 600 parts per million (“ppm”), or even greater, based onthe dry weight of the starting polylactic acid. Moisture content may bedetermined in a variety of ways as is know in the art, such as inaccordance with ASTM D 7191-05, such as described below. Because thepresence of water during melt processing can hydrolytically degrade thepolyester and reduce its molecular weight, it is sometimes desired to,dry the polyester prior to blending. In most embodiments, for example,it is desired that the polyester have a moisture content of about 300parts per million (“ppm”) or less, in some embodiments about 200 ppm orless, in some embodiments from about 1 to about 100 ppm prior toblending with the microinclusion and nanoinclusion additives. Drying ofthe polyester may occur, for instance, at a temperature of from about50° C. to about 100° C., and in some embodiments, from about 70° C. toabout 80° C.

B. Microinclusion Additive

As used herein, the term “'microinclusion additive” generally refers toany material that is capable of being dispersed within the polymermatrix in the form of discrete domains of a micro-scale size. Forexample, prior to drawing, the domains may have an averagecross-sectional dimension of from about 0.05 μm to about 30 μm, in someembodiments from about 0.1 μm to about 25 μm, in some embodiments fromabout 0.5 μm to about 20 μm, and in some embodiments from about 1 μm toabout 10 μm. The term “cross-sectional dimension” generally refers to acharacteristic dimension (e.g., width or diameter) of a domain, which issubstantially orthogonal to its major axis (e.g., length) and alsotypically substantially orthogonal to the direction of the stressapplied during drawing. While typically formed from the microinclusionadditive, it should be also understood that the micro-scale domains mayalso be formed from a combination of the microinclusion andnanoinclusion additives and/or other components of the composition.

The particular nature of the microinclusion additive is not critical,and may include liquids, semi-solids, or solids (e.g., amorphous,crystalline or semi-crystalline). In certain embodiments, themicroinclusion additive is polymeric in nature and possesses arelatively high molecular weight to help improve the melt strength andstability of the thermoplastic composition. Typically, themicroinclusion additive polymer may be generally incompatible with thematrix polymer. In this manner, the additive can better become dispersedas discrete phase domains within a continuous phase of the matrixpolymer. The discrete domains are capable of absorbing energy thatarises from an external force, which increases the overall toughness andstrength of the resulting material. The domains may have a variety ofdifferent shapes, such as elliptical, spherical, cylindrical, plate-liketubular, etc. In one embodiment for example, the domains have asubstantially elliptical shape. The physical dimension of an individualdomain is typically small enough to minimize the propagation of cracksthrough the polymeric material upon the application of an externalstress, but large enough to initiate microscopic plastic deformation andallow for shear and/or stress intensity zones at and around particleinclusions.

While the polymers may be immiscible, the microinclusion additive maynevertheless be selected to have a solubility parameter that isrelatively similar to that of the matrix polymer. This can improve theinterfacial compatibility and physical interaction of the boundaries ofthe discrete and continuous phases, and thus reduces the likelihood thatthe composition will fracture. In this regard, the ratio of thesolubility parameter for the matrix polymer to that of the additive istypically from about 0.5 to about 1.5, and in some embodiments, fromabout 0.8 to about 1.2. For example, the microinclusion additive mayhave a solubility parameter of from about 15 to about 30MJoules^(1/2)/m^(3/2), and in some embodiments, from about 18 to about22 MJoules^(1/2)/m^(3/2), while polylactic acid may have a solubilityparameter of about 20.5 MJoules^(1/2)/m^(3/2). The term “solubilityparameter” as used herein refers to the “Hildebrand SolubilityParameter”, which is the square root of the cohesive energy density andcalculated according to the following equation:

δ=√{square root over (()}(ΔH _(v) −RT)/V _(m))

where:

-   -   Δ Hv=heat of vaporization    -   R=Ideal Gas constant    -   T=Temperature    -   Vm=Molecular Volume

The Hildebrand solubility parameters for many polymers are alsoavailable from the Solubility Handbook of Plastics, by Wyeych (2004),which is incorporated herein by reference.

The microinclusion additive may also have a certain melt flow rate (orviscosity) to ensure that the discrete domains and resulting pores canbe adequately maintained. For example, if the melt flow rate of theadditive is too high, it tends to flow and disperse uncontrollablythrough the continuous phase. This results in lamellar, plate-likedomains or co-continuous phase structures that are difficult to maintainand also likely to prematurely fracture. Conversely, if the melt flowrate of the additive is too low, it tends to clump together and formvery large elliptical domains which are difficult to disperse duringblending. This may cause uneven distribution of the additive through theentirety of the continuous phase. In this regard, the present inventorshave discovered that the ratio of the melt flow rate of themicroinclusion additive to the melt flow rate of the matrix polymer istypically from about 0.2 to about 8, in some embodiments from about 0.5to about 6 and in some embodiments, from about 1 to about 5. Themicroinclusion additive may, for example, have a melt flow rate of fromabout 0.1 to about 250 grams per 10 minutes, in some embodiments fromabout 0.5 to about 200 grams per 10 minutes, and in some embodiments,from about 5 to about 150 grams per 10 minutes, determined at a load of2160 grams and at 190° C.

In addition to the properties noted above, the mechanicalcharacteristics of the microinclusion additive may also be selected toachieve the desired porous network. For example, when a blend of thematrix polymer and microinclusion additive is applied with an externalforce, stress concentrations (e.g. including normal or shear stresses)and shear and/or plastic yielding zones may be initiated at and aroundthe discrete phase domains as a result of stress concentrations thatarise from a difference in the elastic modulus of the additive andmatrix polymer. Larger stress concentrations promote more intensivelocalized plastic flow at the domains, which allows them to becomesignificantly elongated when stresses are imparted. These elongateddomains can allow the composition to exhibit a more pliable and softerbehavior than the matrix polymer, such as when it is a rigid polyesterresin. To enhance the stress concentrations, the microinclusion additivemay be selected to have a relatively low Young's modulus of elasticityin comparison to the matrix polymer. For example, the ratio of themodulus of elasticity of the matrix polymer to that of the additive istypically from about 1 to about 250, in some embodiments from about 2 toabout 100, and in some embodiments, from about 2 to about 50. Themodulus of elasticity of the microinclusion additive may, for instance,range from about 2 to about 1000 Megapascal (MPa), in some embodimentsfrom about 5 to about 500 MPa, and in some embodiments, from about 10 toabout 200 MPa. To the contrary, the modulus of elasticity of polylacticacid, for example is typically from about 800 MPa to about 3000 MPa.

While a wide variety of microinclusion additives may be employed thathave the properties identified above, particularly suitable examples ofsuch additives may include synthetic polymers, such as polyolefins(e.g., polyethylene, polypropylene, polybutylene, etc.); styreniccopolymers (e.g., styrene-butadiene-styrene, styrene-isoprene-styrene,styrene-ethylene-propylene-styrene, styrene-ethylene-butadiene-styrene,etc.); polytetrafluoroethylenes; polyesters (e.g., recycled polyester,polyethylene terephthalate, etc.); polyvinyl acetates (e.g.,poly(ethylene vinyl acetate), polyvinyl chloride acetate, etc.);polyvinyl alcohols (e.g., polyvinyl alcohol, poly(ethylene vinylalcohol), etc); polyvinyl butyrals, acrylic polyacrylate,polymethylacrylate, polymethylmethacrylate, etc.); polyamides (e.g.,nylon); polyvinyl chlorides; polyvinylidene chlorides; polystyrenes;polyurethanes; etc. Suitable polyolefins may, for instance, includeethylene polymers (e.g., low density polyethylene (“LDPE”) high densitypolyethylene (“HDPE”), linear low density polyethylene (“LLDPE”), etc.),propylene homopolymers (e.g., syndiotactic, atactic, isotactic, etc.),propylene copolymers, and so forth.

In one particular embodiment, the polymer is a propylene polymer, suchas homopolypropylene or a copolymer of propylene. The propylene polymermay, for instance, be formed from a substantially isotacticpolypropylene homopolymer or a copolymer containing equal to or lessthan about 10 wt. % of other monomer, i.e., at least about 90% by weightpropylene. Such homopolymers may have a melting point of from about 160°C. to about 170° C.

In still another embodiment, the polyolefin may be a copolymer ethyleneor propylene with another α-olefin, such as a C₃-C₂₀ α-olefin or C₃-C₁₂α-olefin. Specific examples of suitable α-olefins include 1-butene;3-methyl-1-butene; 3,3-dimethyl-1-butene; 1-pentene; 1-pentene with oneor more methyl, ethyl or propyl substituents; 1-hexene with one or moremethyl, ethyl or propyl substituents; 1-heptene with one or more methyl,ethyl or propyl substituents; 1-octene with one or more methyl, ethyl orpropyl substituents; 1-nonene with one or more methyl, ethyl or propylsubstituents; ethyl, methyl or dimethyl-substituted 1-decene;1-dodecene; and styrene. Particularly desired α-olefin comonomers are1-butene, 1-hexene and 1-octene. The ethylene or propylene content ofsuch copolymers may be from about 60 mole % to about 99 mole %, in someembodiments from about 80 mole % to about 98.5 mole %, and in someembodiments, from about 87 mole % to about 97.5 mole %. The α-olefincontent may likewise range from about 1 mole % to about 40 mole %, insome embodiments from about 1.5 mole % to about 15 mole %, and in someembodiments, from about 2.5 mole % to about 13 mole %.

Exemplary olefin copolymers for use in the present invention includeethylene-based copolymers available under the designation EXACT™ fromExxonMobil Chemical Company of Houston, Tex. Other suitable ethylenecopolymers are available under the designation ENGAGE™, AFFINITY™,DOWLEX™ (LLDPE) and ATTANE™ (ULDPE) from Dow Chemical Company ofMidland, Mich. Other suitable ethylene polymers are described in U.S.Pat. No. 4,937,299 to Ewen et al. U.S. Pat. No. 5,218,071 to Tsutsui etal.; U.S. Pat. No. 5,272,236 to Lai, et al.; and U.S. Pat. No. 5,278,272to Lai, et al. Suitable propylene copolymers are also commerciallyavailable under the designations VISTAMAXX™ from ExxonMobil Chemical Co.of Houston, Tex.; FINA™ (e.g., 8573) from Atofina Chemicals of Feluy,Belgium; TAFMER™ available from Mitsui Petrochemical Industries; andVERSIFY™ available from Dow Chemical Co. of Midland, Mich. Suitablepolypropylene homopolymers may likewise include Exxon Mobil 3155polypropylene, Exxon Mobil Achieve™ resins, and Total M3661 PP resinOther examples of suitable propylene polymers are described in U.S. Pat.No. 6,500,563 to Datta et a U.S. Pat. No. 5,539,056 to Yang, et al,; andU.S. Pat. No. 5,596,052 to Resconi, et al.

Any of a variety of known techniques may generally be employed to formthe olefin copolymers. For instance, olefin polymers may be formed usinga free radical or a coordination catalyst (e.g., Ziegler-Natta).Preferably, the olefin polymer is formed from a single-site coordinationcatalyst such as a metallocene catalyst. Such a catalyst system producesethylene copolymers in which the comonomer is randomly distributedwithin a molecular chain and uniformly distributed across the differentmolecular weight fractions Metallocene-catalyzed polyolefins aredescribed, for instance, in U.S. Pat. No. 5,571,619 to McAlpin et al.;U.S. Pat. No. 5,322,728 to Davis et at U.S. Pat. No. 5,472,775 toObijeski et al.; U.S. Pat. No. 5,272,236 to Lai et al.; and U.S. Pat.No. 6,090,325 to Wheat, et al. Examples of metallocene catalysts includebis(n-butylcyclopentadienylyl)titanium dichloride,bis(n-butylcyclopentadienyl)zirconium dichloride,bis(cyclopentadienyl)scandium chloride, bis(indenyl)zirconiumdichloride, bis(methylcyclopentadienyl)titanium dichloride,bis(methylcyclopentadienyl)zirconium dichloride, cobaltocene,cyclopentadienyltitanium trichloride, ferrocene, hafnocene dichloride,isopropyl(cyclopentedienyl,-1-flourenyl)zirconium dichloride,molybdocene dichloride, nickelocene, niobocene dichloride, ruthenocene,titanocene dichloride, zirconocene chloride hydride, zirconocenedichloride, and so forth. Polymers made using metallocene catalyststypically have a narrow molecular weight rang For instance,metallocene-catalyzed polymers may have polydispersity numbers(M_(w)/M_(n)) of below 4, controlled short chain branching distribution,and controlled isotacticity.

Regardless of the materials employed, the relative percentage of themicroinclusion additive in the thermoplastic composition is selected toachieve the desired properties without significantly impacting the baseproperties of the composition. For example, the microinclusion additiveis typically employed in an amount of from about 1 wt. % to about 30 wt.%, in some embodiments from about 2 wt. % to about 25 wt. %, and in someembodiments, from about 5 wt. % to about 20 wt. % of the thermoplasticcomposition, based on the weight of the continuous phase (matrixpolymer(s)). The concentration of the microinclusion additive in theentire thermoplastic composition may likewise constitute from about 0.1wt. % to about 30 wt. % in some embodiments from about 0.5 wt. % toabout 25 wt. %, and in some embodiments, from about 1 wt. % to about 20wt. %.

C. Nanoinclusion Additive

As used herein, the term “nanoinclusion additive” generally refers to amaterial that is capable of being dispersed within the polymer matrix inthe form of discrete domains of a nano-scale size. For example, prior todrawing, the domains may have an average cross-sectional dimension offrom about 1 to about 1000 nanometers, in some embodiments from about 5to about 800 nanometers in some embodiments from about 10 to about 500nanometers, and in some embodiments from about 20 to about 200nanometers. It should be also understood that the nano-scale domains mayalso be formed from a combination of the microinclusion andnanoinclusion additives and/or other components of the composition. Thenanoinclusion additive is typically employed in an amount of from about0.05 wt. % to about 20 wt. % in some embodiments from about 0.1 wt. % toabout 10 wt. %, and in some embodiments, from about 0.5 wt. % to about 5wt. % of the thermoplastic composition, based on the weight of thecontinuous phase (matrix polymer(s)). The concentration of thenanoinclusion additive in the entire thermoplastic composition maylikewise be from about 0.01 wt. % to about 15 wt. %, in some embodimentsfrom about 0.05 wt. % to about 10 wt. %, and in some embodiments, fromabout 0.3 wt. % to about 6 wt. % of the thermoplastic composition.

The particular state or form of the nanoinclusion additive is notcritical so long as the desired domains can be formed. For example, insome embodiments, the nanoinclusion additive can be in the form of aliquid or semi-solid at room temperature (e.g., 25° C.) Such a liquidcan be readily dispersed in the matrix to form a metastable dispersion,and then quenched to preserve the domain size by reducing thetemperature of the blend. In yet other embodiments, the nanoinclusionadditive is in the form of a solid, which may be amorphous crystalline,or semi-crystalline. For example, the nanoinclusion additive may bepolymeric in nature and possess a relatively high molecular weight tohelp improve the melt strength and stability of the thermoplasticcomposition.

To enhance its ability to become dispersed into nano-scale domains, thenanoinclusion additive may contain a polar component that is compatiblewith a portion of the matrix polymer and/or the microinclusion additive.This may be particularly useful when the matrix polymer or themicroinclusion additive possesses a polar moiety, such as a polyester.One example such a nanoinclusion additive is a functionalizedpolyolefin. The polar component may, for example, be provided by one ormore functional groups and the non-polar component may be provided by anolefin. The olefin component of the nanoinclusion additive may generallybe formed from any linear or branched α-olefin monomer, oligomer, orpolymer (including copolymers) derived from an olefin monomer, such asdescribed above.

The functional group of the nanoinclusion additive may be any group,molecular segment and/or block that provides a polar component to themolecule and is not compatible with the matrix polymer. Examples ofmolecular segment and/or blocks not compatible with polyolefin mayinclude acrylates, styrenics, polyesters, polyamides, etc. Thefunctional group can have an ionic nature and comprise charged metalions. Particularly suitable functional groups are maleic anhydride,maleic acid, fumaric acid, maleimide, maleic acid hydrazide, a reactionproduct of maleic anhydride and diamine, methylnadic anhydride,dichloromaleic anhydride, maleic acid amide, etc. Maleic anhydridemodified polyolefins are particularly suitable for use in the presentinvention. Such modified polyolefins are typically formed by graftingmaleic anhydride onto a polymeric backbone material. Such maleatedpolyolefins are available from E. I. du Pont de Nemours and Companyunder the designation Fusabond®. such as the P Series (chemicallymodified polypropylene), E Series (chemically modified polyethylene), CSeries (chemically modified ethylene vinyl acetate), A Series(chemically modified ethylene acrylate copolymers or terpolymers), or NSeries (chemically modified ethylene-propylene ethylene-propylene dienemonomer (“EPDM”) or ethylene-octene). Alternatively, maleatedpolyolefins are also available from Chemtura Corp. under the designationPolybond® and Eastman Chemical Company under the designation Eastman Gseries.

In certain embodiments, the nanoinclusion additive may also be reactive.One example of such a reactive nanoinclusion additive is a polyepoxidethat contains, on average, at least two oxirane rings per molecule.Without intending to be limited by theory, it is believed that suchpolyepoxide molecules can induce reaction of the matrix polymer (e.g.,polyester) under certain conditions, thereby improving its melt strengthwithout significantly reducing glass transition temperature. Thereaction may involve chain extension, side chain branching graftingcopolymer formation, etc. Chain extension for instance, may occurthrough a variety of different reaction pathways. For instance, themodifier may enable a nucleophilic ring-opening reaction via a carboxylterminal group of a polyester (esterification) or via a hydroxyl group(etherification). Oxazoline side reactions may likewise occur to formesteramide moieties. Through such reactions, the molecular weight of thematrix polymer may be increased to counteract the degradation oftenobserved during melt processing. While it may be desirable to induce areaction with the matrix polymer as described above, the presentinventors have discovered that too much of a reaction can lead tocrosslinking between polymer backbones. If such crosslinking is allowedto proceed to a significant extent, the resulting polymer blend canbecome brittle and difficult to process into a material with the desiredstrength and elongation properties.

In this regard, the present inventors have discovered that polyepoxidehaving a relatively low epoxy functionality are particularly effective,which may be quantified by its “epoxy equivalent weight.” The epoxyequivalent weight reflects the amount of resin that contains onemolecule of an epoxy group, and it may be calculated by dividing thenumber average molecular weight of the modifier by the number of epoxygroups in the molecule. The polyepoxide of the present inventiontypically has a number average molecular weight from about 7,500 toabout 250,000 grams per mole, in some embodiments from about 15,000 toabout 150,000 grams per mole, and in some embodiments, from about 20,000to 100,000 grams per mole, with a polydispersity index typically rangingfrom 2.5 to 7, The polyepoxide may contain less than 50 in someembodiments from 5 to 45, and in some embodiments, from 15 to 40 epoxygroups. <In turn, the epoxy equivalent weight may be less than about15,000 grams per mole, in some embodiments from about 200 to about10,000 grams per mole, and in some embodiments, from about 500 to about7,000 grams per mole.

The polyepoxide may be a linear or branched, homopolymer or copolymer(e.g., random, graft, block, etc.) containing terminal epoxy groupsskeletal oxirane units, and/or pendent epoxy groups. The monomersemployed to form such polyepoxides may vary. In one particularembodiment, for example, the polyepoxide contains at least oneepoxy-functional (meth)acrylic monomeric component. As used herein, theterm “(meth)acrylic” includes acrylic and methacrylic monomers, as wellas salts or esters thereof, such as acrylate and methacrylate monomers.For example, suitable epoxy-functional (meth)acrylic monomers mayinclude, but are not limited to, those containing 1,2-epoxy groups, suchas glycidyl acrylate and glycidyl methacrylate. Other suitableepoxy-functional monomers include allyl glycidyl ether, glycidylethacrylate, and glycidyl itoconate.

The polyepoxide typically has a relatively high molecular weight, asindicated above, so that it may not only result in chain extension, butalso help to achieve the desired blend morphology. The resulting meltflow rate of the polymer is thus typically within a range of from about10 to about 200 grams per 10 minutes, in some embodiments from about 40to about 150 grams per 10 minutes, and in some embodiments, from about60 to about 120 grams per 10 minutes, determined at a load of 2160 gramsand at a temperature of 190° C.

If desired, additional monomers may also be employed in the polyepoxideto help achieve the desired molecular weight. Such monomers may vary andinclude, for example, ester monomers, (meth)acrylic monomers, olefinmonomers, amide monomers, etc. In one particular embodiment, forexample, the polyepoxide includes at least one linear or branchedα-olefin monomer, such as those having from 2 to 20 carbon atoms andpreferably from 2 to 8 carbon atoms. Specific examples include ethylene,propylene, 1-butene; 3-methyl-1-butene; 3,3-dimethyl-1-butene;1-pentene; 1-pentene with one or more methyl, ethyl or propylsubstituents; 1-hexene with one or more methyl, ethyl or propylsubstituents; 1-heptene with one or more methyl, ethyl or propylsubstituents; 1-octene with one or more methyl, ethyl or propylsubstituents; 1-nonene with one or more methyl, ethyl or propylsubstituents; ethyl, methyl or dimethyl-substituted 1-decene;1-dodecene; and styrene. Particularly desired α-olefin comonomers areethylene and propylene.

Another suitable monomer may include a (meth)acrylic monomer that is notepoxy-functional. Examples of such (meth)acrylic monomers may includemethyl acrylate, ethyl acrylate n-propyl acrylate, i-propyl acrylate,n-butyl acrylate, s-butyl acrylate, i-butyl acrylate, t-butyl acrylate,n-amyl acrylate, i-amyl acrylate, isobornyl acrylate, n-hexyl acrylate,2-ethylbutyl acrylate, 2-ethylhexyl acrylate, n-octyl acrylate, n-decylacrylate, methylcyclohexyl acrylate, cyclopentyl acrylate, cyclohexylacrylate, methyl methacrylate, ethyl methacrylate, 2-hydroxyethylmethacrylate, n-propyl methacrylate, n-butyl methacrylate, i-propylmethacrylate, i-butyl methacrylate, n-amyl methacrylate n-hexylmethacrylate, i-amyl methacrylate, s-butyl-methacrylate, t-butylmethacrylate, 2-ethylbutyl methacrylate, methylcyclohexyl methacrylate,cinnamyl methacrylate, crotyl methacrylate, cyclohexyl methacrylate,cyclopentyl methacrylate, 2-ethoxyethyl methacrylate, isobornylmethacrylate, etc., as well as combinations thereof.

In one particularly desirable embodiment of the present invention, thepolyepoxide is a terpolymer formed from an epoxy-functional(meth)acrylic monomeric component, α-olefin monomeric component, andnon-epoxy functional (meth)acrylic monomeric component. For example thepolyepoxide may be poly(ethylene-co-methylacrylate-co-glycidylmethacrylate), which has the following structure:

wherein, x, y, and z are 1 or greater.

The epoxy functional monomer may be formed into a polymer using avariety of known techniques. For example, a monomer containing polarfunctional groups may be grafted onto a polymer backbone to form a graftcopolymer. Such grafting techniques are well known in the art anddescribed, for instance, in U.S. Pat. No. 5,179,164. In otherembodiments, a monomer containing epoxy functional groups may becopolymerized with a monomer to form a block or random copolymer usingknown free radical polymerization techniques, such as high pressurereactions. Ziegler-Natta catalyst reaction systems, single site catalyst(e.g., metallocene) reaction systems, etc.

The relative portion of the monomeric component(s) may be selected toachieve a balance between epoxy-reactivity and melt flow rate. Moreparticularly, high epoxy monomer contents can result in good activitywith the matrix polymer, but too high of a content may reduce the meltflow rate to such an extent that the polyepoxide adversely impacts themelt strength of the polymer blend. Thus, in most embodiments, theepoxy-functional (meth)acrylic monomer(s) constitute from about 1 wt. %to about 25 wt. %, in some embodiments from about 2 to about 20 wt. %,and in some embodiments, from about 4 wt. % to about 15 wt. % of thecopolymer, The α-olefin monomer(s) may likewise constitute from about 55wt. % to about 95 wt. %, in some embodiments from about 60 wt. % toabout 90 wt %, and in some embodiments, from about 65 wt. % to about 85wt. % of the copolymer. When employed, other monomeric components (e.g.,non-epoxy functional meth)acrylic monomers) may constitute from about 5wt. % to about 35 wt. %, in some embodiments from about 8 wt. % to about30 wt. %, and in some embodiments, from about 10 wt. % to about 25 wt. %of the copolymer. One specific example of a suitable polyepoxide thatmay be used in the present invention is commercially available fromArkema under the name LOTADER® AX8950 or AX8900. LOTADER® AX8950, forinstance, has a melt flow rate of 70 to 100 g/10 min and has a glycidylmethacrylate monomer content of 7 wt. % to 11 wt. %, a methyl acrylatemonomer content of 13 wt. % to 17 wt. %, and an ethylene monomer contentof 72 wt. % to 80 wt. %. Another suitable polyepoxide is commerciallyavailable from DuPont under the name ELVALOY® PTW, which is a terpolymerof ethylene, butyl acrylate, and glycidyl methacrylate and has a meltflow rate of 12 g/10 min.

In addition to controlling the type and relative content of the monomersused to form the polyepoxide, the overall weight percentage may also becontrolled to achieve the desired benefits. For example, if themodification level is too low, the desired increase in melt strength andmechanical properties may not be achieved. The present inventors havealso discovered, however, that if the modification level is too high,processing may be restricted due to strong molecular interactions (e.g.,crosslinking) and physical network formation by the epoxy functionalgroups. Thus, the polyepoxide is typically employed in an amount of fromabout 0.05 wt. % to about 10 wt. %, in some embodiments from about 0.1wt. % to about 8 wt. %, in some embodiments from about 0.5 wt. % toabout 5 wt. %, and in some embodiments, from about 1 wt. % to about 3wt. %, based on the weight of the matrix polymer employed in thecomposition. The polyepoxide may also constitute from about 0.05 wt. %to about 10 wt. % in some embodiments from about 0.0 wt. % to about 8wt. %, in some embodiments from about 0.1 wt. % to about 5 wt. %, and insome embodiments, from about 0.5 wt. % to about 3 wt. % based on thetotal weight of the composition.

Other reactive nanoinclusion additives may also be employed in thepresent invention, such as oxazoline-functionalized polymers,cyanide-functionalized polymers, etc. When employed, such reactivenanoinclusion additives may be employed within the concentrations notedabove for the polyepoxide. In one particular embodiment, anoxazoline-grafted polyolefin may be employed that is a polyolefingrafted with an oxazoline ring-containing monomer. The oxazoline mayinclude a 2-oxazoline, such as 2-vinyl-2-oxazoline (e.g.,2-isopropenyl-2-oxazoline), 2-fatty-alkyl-2-oxazoline (e.g., obtainablefrom the ethanolamide of oleic acid, linoleic acid, palmitoleic acidgadoleic acid, erucic acid and/or arachidonic acid) and combinationsthereof. In another embodiment, the oxazoline may be selected fromricinoloxazoline maleinate, undecyl-2-oxazoline, soya-2-oxazoline,ricinus-2-oxazoline and combinations thereof, for example. In yetanother embodiment, the oxazoline is selected from2-isopropenyl-2-oxazoline, 2-isopropenyl-4,4-dimethyl-2-oxazoline andcombinations thereof.

Nanofillers may also be employed, such as carbon black, carbonnanotubes, carbon nanofibers, nanoclays, metal nanoparticles,nanosilica, nanoalumina, etc. Nanoclays are particularly suitable. Theterm “nanoclay” generally refers to nanoparticles of a clay material (anaturally occurring mineral, an organically modified mineral, or asynthetic nanomaterial), which typically have a platelet structure.Examples of nanoclays include, for instance, montmorillonite (2:1layered smectite clay structure), bentonite (aluminium phyllosilicateformed primarily of montmorillonite), kaolinite (1:1 aluminosilicatehaving a platy structure and empirical formula of Al₂Si₂O₅(OH)₄)halloysite (1:1 aluminosilicate having a tubular structure and empiricalformula of Al₂Si₂O₅(OH)₄), etc. An example of a suitable nanoclay isCloisite®, which is a montmorillonite nanoclay and commerciallyavailable from Southern Clay Products, Inc. Other examples of synthethicnanoclays include but are not limited to a mixed-metal hydroxidenanoclay, layered double hydroxide nanoclay (e.g., sepiocite), laponite,hectorite, saponite, indonite, etc.

If desired, the nanoclay may contain a surface treatment to help improvecompatibility with the matrix polymer (e.g., polyester). The surfacetreatment may be organic or inorganic. In one embodiment, an organicsurface treatment is employed that is obtained by reacting an organiccation with the clay. Suitable organic cations may include, forinstance, organoquaternary ammonium compounds that a re capable ofexchanging cations with the clay, such as dimethyl bis[hydrogenatedtallow] ammonium chloride (2M2HT), methyl benzyl bis[hydrogenatedtallow] ammonium chloride (MB2HT), methyl tris[hydrogenated tallowalkyl] chloride (M3HT), etc. Examples of commercially available organicnanoclays may include, for instance, Dellite® 43B (Laviosa Chimica ofLivorno, Italy), which is a montmorillonite clay modified with dimethylbenzylhydrogenated tallow ammonium salt. Other examples includeCloisite® 25A and Cloisite® 30B (Southern Clay Products) and Nanofil 919(Süd Chemie). If desired, the nanofiller can be blended with a carrierresin to form a masterbatch that enhances the compatibility of theadditive with the other polymers in the composition. Particularlysuitable carrier resins include, for instance, polyesters (e.g.,polylactic acid, polyethylene terephthalate, etc.); polyolefins (e.g.,ethylene polymers, propylene polymers etc.); and so forth, as describedin more detail above.

In certain embodiments of the present invention, multiple nanoinclusionadditives may be employed in combination. For instance, a firstnanoinclusion additive (e.g., polyepoxide) may be dispersed in the formof domains having an average cross-sectional dimension of from about 50to about 500 nanometers, some embodiments from about 60 to about 400nanometers, and in some embodiments from about 80 to about 300nanometers. A second nanoinclusion additive (e.g., nanofiller) may alsobe dispersed in the form of domains that are smaller than the firstnanoinclusive additive, such as those having an average cross-sectionaldimension of from about 1 to about 50 nanometers, in some embodimentsfrom about 2 to about 45 nanometers, and in some embodiments from about5 to about 40 nanometers. When employed, the first and/or secondnanoinclusion additives typically constitute from about 0.05 wt. % toabout 20 wt. % in some embodiments from about 0.1 wt. % to about 10 wt.%, and in some embodiments, from about 0.5 wt. % to about 5 wt. % of thethermoplastic composition, based on the weight of the continuous phase(matrix polymer(s)). The concentration of the first and/or secondnanonclusion additives in the entire thermoplastic composition maylikewise be from about 0.01 wt. % to about 15 wt. %, in some embodimentsfrom about 0.05 wt. % to about 10 wt. %, and in some embodiments, fromabout 0.1 wt. % to about 8 wt. % of the thermoplastic composition.

D. Other Components

A wide variety of ingredients may be employed in the composition for avariety of different reasons. For instance, in one particularembodiment, an interphase modifier may be employed in the thermoplasticcomposition to help reduce the degree of friction and connectivitybetween the microinclusion additive and matrix polymer, and thus enhancethe degree and uniformity of debonding. In this manner, the pores canbecome distributed in a more homogeneous fashion throughout thecomposition. The modifier may be in a liquid or semi-solid form at roomtemperature (e.g., 25° C.) so that it possesses a relatively lowviscosity, allowing it to be more readily incorporated into thethermoplastic composition and to easily migrate to the polymer surfaces.In this regard, the kinematic viscosity of the interphase modifier istypically from about 0.7 to about 200 centistokes (“cs”), in someembodiments from about 1 to about 100 cs, and in some embodiments, fromabout 1.5 to about 80 cs, determined at 40° C. In addition, theinterphase modifier is also typically hydrophobic so that it has anaffinity for the microinclusion additive, for example, resulting in achange in the interfacial tension between the matrix polymer and theadditive. By reducing physical forces at the interfaces between thematrix polymer and the microinclusion additive, it is believed that thelow viscosity, hydrophobic nature of the modifier can help facilitatedebonding. As used herein, the term “hydrophobic” typically refers to amaterial having a contact angle of water in air of about 40° or more,and in some cases, about 60° or more In contrast, the term “hydrophilic”typically refers to a material having a contact angle of water in air ofless than about 40°. One suitable test for measuring the contact angleis ASTM D5725-99 (2008).

Suitable hydrophobic, low viscosity interphase modifiers may include,for instance, silicones, silicone-polyether copolymers, aliphaticpolyesters, aromatic polyesters, alkylene glycols (e, g., ethyleneglycol, diethylene glycol, triethylene glycol, tetraethylene glycol,propylene glycol, polyethylene glycol, polypropylene glycol,polybutylene glycol, etc.), alkane diols (e.g., 1,3-propanediol,2,2-dimethyl-1,3-propanediol, 1,3-butanediol, 1,4-butanediol,1,5-pentanediol, 1,6-hexanediol, 2,2,4-trimethyl-1,6 hexanediol, 1,3cyclohexanedimethanol, 1,4-cyclohexanedimethanol,2,2,4,4-tetramethyl-1,3-cyclobutanediol, etc.), amine oxides (e.g.,octyldimethylamine oxide) fatty acid esters, etc. One particularlysuitable interphase modifier is polyether polyol, such as commerciallyavailable under the trade name PLURIOL® WI from BASF Corp, Anothersuitable modifier is a partially renewable ester, such as commerciallyavailable under the trade name HALLGREEN® IM from Hallstar.

When employed, the interphase modifier may constitute from about 0.1 toabout 20 wt. %, in some embodiments from about 0.5 wt. % to about 15 wt.%, and in some embodiments, from about 1 wt. % to about 10 wt. % of thethermoplastic composition, based on the weight of the continuous phase(matrix polymer(s)). The concentration of the interphase modifier in theentire thermoplastic composition may likewise constitute from about 0.05wt. % to about 20 wt. %, in some embodiments from about 0.1 wt. % toabout 15 wt. %, and in some embodiments, from about 0.5 wt. % to about10 wt. %.

When employed in the amounts noted above, the interphase modifier has acharacter that enables it to readily migrate to the interfacial surfaceof the polymers and facilitate debonding without disrupting the overallmelt properties of the thermoplastic composition. For example, theinterphase modifier does not typically have a plasticizing effect on thepolymer by reducing its glass transition temperature. Quite to thecontrary, the present inventors have discovered that the glasstransition temperature of the thermoplastic composition may besubstantially the same as the initial matrix polymer. In this regard,the ratio of the glass temperature of the composition to that of thematrix polymer is typically from about 0.7 to about 1.3, in someembodiments from about 0.8 to about 1.2, and in some embodiments, fromabout 0.9 to about 1.1. The thermoplastic composition may, for example,have a glass transition temperature of from about 35° C. to about 80°C., in some embodiments from about 40° C. to about 80° C., and in someembodiments, from about 50° C. to about 65° C. The melt flow rate of thethermoplastic composition may also be similar to that of the matrixpolymer. For example, the melt flow rate of the composition (on a drybasis) may be from about 0.1 to about 70 grams per 10 minutes, in someembodiments from about 0.5 to about 50 grams per 10 minutes, and in someembodiments, from about 5 to about 25 grams per 10 minutes, determinedat a load of 2160 prams and at a temperature of 190° C.

Compatibilizers may also be employed that improve interfacial adhesionand reduce the interfacial tension between the domain and the matrix,thus allowing the formation of smaller domains during mixing. Examplesof suitable compatibilizers may include, for instance, copolymersfunctionalized with epoxy or maleic anhydride chemical moieties. Anexample of a maleic anhydride compatibilizer is polypropylene-graftedmaleic anhydride which is commercially available from Arkema under thetrade names Orevac™ 18750 and Orevac™ CA 100. When employed,compatibilizers may constitute from about 0.05 wt. % to about 10 wt. %,in some embodiments from about 0.1 wt. % to about 8 wt. %, and in someembodiments, from about 0.5 wt. % to about 5 wt. % of the thermoplasticcomposition, based on the weight of the continuous phase matrix.

Other suitable materials that may also be used in the thermoplasticcomposition, such as catalysts, antioxidants, stabilizers, surfactants,waxes, solid solvents, fillers, nucleating agents (e.g. calciumcarbonate, etc.), particulates, and other materials added to enhance theprocessability and mechanical properties of the thermoplasticcomposition. Nevertheless, one beneficial aspect of the presentinvention is that good properties may be provided without the need forvarious conventional additives, such as blowing agents (e.g.,chlorofluorocarbons, hydrochlorofluorocarbons, hydrocarbons, carbondioxide, supercritical carbon, dioxide, nitrogen, etc.) and plasticizers(e.g., solid or semi-solid polyethylene glycol). In fact, thethermoplastic composition may be generally free of blowing agents and/orplasticizers. For example blowing agents and/or plasticizers may bepresent in an amount of no more than about 1 wt. %, in some embodimentsno more than about 0.5 wt. %, and in some embodiments from about 0.001wt. % to about 0.2 wt. % of the thermoplastic composition. Further, dueto its stress whitening properties, as described in more detail below,the resulting composition may achieve an opaque color (e.g., white)without the need for conventional pigments, such as titanium dioxide. Incertain embodiments, for example, pigments may be present in an amountof no more than about 1 wt. %, in some embodiments no more than about0.5 wt %, and in some embodiments, from about 0.001 wt. % to about 0.2wt. % of the thermoplastic composition.

II. Blending

Prior to initiating pores in the composition, the components aretypically blended together using any of a variety of known techniques.In one embodiment, for example, the components may be suppliedseparately or in combination. For instance, the components may first bedry mixed together to form an essentially homogeneous dry mixture, andthey may likewise be supplied either simultaneously or in sequence to amelt processing device that dispersively blends the materials. Batchand/or continuous melt processing techniques may be employed. Forexample, a mixer/kneader, Banbury mixer, Farrel continuous mixer,single-screw extruder, twin-screw extruder, roll mill, etc., may beutilized to blend and melt process the materials. Particularly suitablemelt processing devices may be a co-rotating, twin-screw extruder (e.g.,ZSK-30 extruder available from Werner & Pfleiderer Corporation ofRamsey, N.J. or a Thermo Prism™ USALAB 16 extruder available from ThermoElectron Corp., Stone, England). Such extruders may include feeding andventing ports and provide high intensity distributive and dispersivemixing. For example, the components may be fed to the same or differentfeeding ports of the twin-screw extruder and melt blended to form asubstantially homogeneous melted mixture. If desired, other additivesmay also be injected into the polymer melt and/or separately fed intothe extruder at a different point along its length.

Regardless of the particular processing technique chosen, the resultingmelt blended composition typically contains micro-scale domains of themicroinclusion additive and nano-scale domains of the nanoinclusionadditive as described above. The degree of shear/pressure and heat maybe controlled to ensure sufficient dispersion, but not so high as toadversely reduce the size of the domains so that they are incapable ofachieving the desired properties. For example, blending typically occursat a temperature of from about 180° C. to about 300° C., in someembodiments from about 185° C. to about 250° C., and in some embodimentsfrom about 190° C. to about 240° C. Likewise, the apparent shear rateduring melt processing may range from about 10 seconds⁻¹ to about 3000seconds⁻¹, in some embodiments from about 50 seconds⁻¹ to about 2000seconds⁻¹, and in some embodiments, from about 100 seconds⁻¹ to about1200 seconds⁻¹. The apparent shear rate may be equal to 4 Q/π⁻¹R³, whereQ is the volumetric flow rate (“m³/s”) of the polymer melt and is theradius (“m”) of the capillary (e.g., extruder die) through which themelted polymer flows. Of course, other variables, such as the residencetime during melt processing, which is inversely proportional tothroughput rate, may also be controlled to achieve the desired degree ofhomogeneity.

To achieve the desired shear conditions (e.g., rate, residence time,shear rate, melt processing temperature, etc.), the speed of theextruder screw(s) may be selected with a certain range. Generally, anincrease in product temperature is observed with increasing screw speeddue to the additional mechanical energy input into the system. Forexample, the screw speed may range from about 50 to about 600revolutions per minute (“rpm”), in some embodiments from about 70 toabout 500 rpm, and in some embodiments, from about 100 to about 300 rpm.This may result in a temperature that is sufficient high to disperse themicroinclusion additive without adversely impacting the size of theresulting domains. The melt shear rate and in turn the degree to whichthe additives are dispersed, may also be increased through the use ofone or more distributive and/or dispersive mixing, elements within themixing section of the extruder. Suitable distributive mixers for singlescrew extruders may include, for instance, Saxon, Dulmage, CavityTransfer mixers, etc. Likewise, suitable dispersive mixers may includeBlister ring, Leroy/Maddock, CRD mixers, etc. As is well known in theart, the mixing may be further improved by using pins in the barrel thatcreate a folding and reorientation of the polymer melt, such as thoseused in Buss Kneader extruders, Cavity Transfer mixers, and VortexIntermeshing Pin (VIP) mixers.

III. Pore Initiation

Once blended, the porous network structure is introduced by mechanicaldrawing of the composition. Drawing may occur in any direction, such asthe longitudinal direction (e.g., machine direction) transversedirection (e.g., cross-machine direction), etc., as well as combinationsthereof. To perform the desired drawing, the thermoplastic compositionmay be formed into a precursor shape, drawn, and thereafter convertedinto the desired material (e.g., film, fiber, etc.). In one embodiment,the precursor shape may be a film having a thickness of from about 1 toabout 5000 micrometers, in some embodiments from about 2 to about 4000micrometers, in some embodiments from about 5 to about 2500 micrometersand in some embodiments, from about 10 to about 500 micrometers. As analternative to forming a precursor shape, the thermoplastic compositionmay also be drawn in situ as it is being shaped into the desired formfor the polymeric material. In one embodiment, for example, thethermoplastic composition may be drawn as it is being formed into a filmor fiber.

Regardless, various mechanical drawing techniques may be employed. Onesuitable mechanical drawing technique, for instance, a nip roll processin which the material is passed between a nip defined between two rolls,at least one of which is rotatable. In one embodiment, at least one ofthe rolls contains a pattern of raised embossing elements, which cancreate a local deformation in the material. The other roll may likewisebe patterned or smooth (e.g., anvil roll). the deformed areas arestressed to a level above the cavitational yield stress, these areas canform initial pores. When subjected to further drawing stress, the poresareas will grow in size before the remaining material cavitates. Theoverall embossing pattern may be selectively controlled to achieve thedesired pore formation. In one embodiment, for example, an embossingpattern is selected in which the longitudinal axis (longest dimensionalong a center line of the element) of one or more of the elements isskewed relative to the machine direction (“MD”) of the elastic film. Forexample, one or more of the embossing elements may be oriented fromabout 30° to about 150° in some embodiments from about 45° to about135°, and in some embodiments, from about 60° to about 120° relative tothe machine direction of the polymeric material. In this manner, theembossing elements will present a relatively large surface to thematerial in a direction substantially perpendicular to that which itmoves. This increases the area over which shear stress parted and, inturn, facilitates pore formation The pattern of the embossing elementsis generally selected so that the polymeric material has a totalembossing area of less than about 50% (as determined by conventionaloptical microscopic methods) and in some embodiments, less than about30%.

Another suitable nip roll process involves the use of a grooved rollthrough which the polymeric material is able to course. Referring toFIGS. 1-2, for instance, one embodiment of a grooved roll drawingprocess is shown in which a polymeric material 40 (FIG. 2) may bemechanically drawn using satellite rolls 82 that engage an anvil roll84. Specifically, the polymeric material 40 is passed through a nipformed between each satellite roll 82 and the anvil roll 84 so that thepolymeric material 40 is mechanically (incrementally) stretched in across-machine direction. The satellite rolls 82 and anvil roll 84include a plurality of ridges 83 defining a plurality of grooves 85positioned across the grooved rolls in the cross-machine direction. Thegrooves 85 are generally oriented perpendicular to the direction ofstretch of the material. In other words, the grooves 85 are oriented inthe machine direction to stretch the polymeric material 40 in thecross-machine direction. The grooves 85 may likewise be oriented in thecross-machine direction to stretch the polymeric material 40 in themachine direction. The ridges 83 of satellite roll 82 intermesh with thegrooves 85 of anvil roll 84, and the grooves 85 of satellite roll 82intermesh with the ridges 83 of anvil roll 84.

The dimensions and parameters of the, grooves 85 and ridges 83 may havea substantial impact on the degree of pore initiation, provided by therolls 82 and 84. For example, the number of grooves 85 contained on aroll may generally range from about 3 and 15 grooves per inch, in someembodiments from about 5 and 12 grooves, per inch, and in someembodiments from about 5 and 10 grooves per inch. The grooves 85 mayalso have a certain depth “D”, which generally ranges from about 0.25 toabout 1.0 centimeter, and in some embodiments, from about 0.4 to about0.6 centimeters. In addition, the peak-to-peak distance “P” between thegrooves 85 is typically from about 0.1 to about 0.9 centimeters, and insome embodiments, from about 0.2 to about 0.5 centimeters. Also, thegroove roll engagement distance “E” between the grooves 85 and ridges 83may be up to about 0.8 centimeters, and in some embodiments, from about0.15 to about 0.4 centimeters.

Besides the use of a nip, the rotational velocity of the rollsthemselves may also be utilized to help impart the desired degree ofmechanical stress. In one embodiment, for example, the material ispassed over a series of rolls that progressively draw the material. Onesuch suitable method for accomplishing such drawing is rough the use ofa machine direction orienter (“MDO”). MDO units typically have aplurality of rolls (e.g., from 5 to 8) that can progressively draw andthe polymeric material in the machine direction. The material may bedrawn in either single or multiple discrete drawing operations. Itshould be noted that some of the rolls in an MDO apparatus may not beoperating at progressively higher speeds. To draw the material in themanner described above, it is typically desired that the rolls of theMDO are not heated. Nevertheless, if desired, one or more rolls may beheated to a slight extent to facilitate the drawing process so long asthe temperature of the composition remains below the ranges noted above.

Of course, it should be understood that rotatable rolls are by no meansrequired to mechanically draw the polymeric material. Die drawing, forinstance, may be employed to mechanically draw the material. In atypical die drawing process, the material is initially extruded into aprecursor shape (e.g., profile) and quenched. The precursor is thenmechanically drawn through a converging die while in a solid state. Oneparticularly suitable die drawing process is pultrusion, during whichthe material is drawn or pulled through the die to form an engineeredprofile or shape determined by the shape of the die. Apart from diedrawing, other mechanical drawing techniques may also be employed, suchas stamping, sheet drawing, etc. In one embodiment, for instance, sheetdrawing may be employed, such as tenter frame drawing, brake drawing,etc. In one particular embodiment, for instance, the polymeric materialmay be mechanically drawn in the form of a sheet u sing a mechanical,electrical, hydraulic or pneumatic brake assembly. The brake assemblymay include a surface where the material is initially placed, a clampingbar, and a bending member that is lifted to create a bend in thematerial. More particularly, the brake assembly may include a pluralityof generally c-shaped members that each present opposing clampingsurfaces for receiving a polymeric material. Furthermore, a socketconnection may be employed to rotatably support the bending member forbending the material disposed between the clamping surfaces. The socketconnection generally includes a male portion and a female portion insliding engagement with one another or connected by a pin hingeconnection to one another. Such brake assemblies are known in the artand described in more detail in, for instance, U.S. Pat. No. 4,282,735to Break; U.S. Pat. No. 4,557 132 to Break. and to U.S. Pat. No.6,389,864 to Chubb.

Yet another technique for mechanically drawing the polymer materialinvolves the use of a fluidic medium (e.g., gas) to impart the desireddegree of energy and stress to the material. One such process is, forinstance, aspiration, which typically involves the use of blown air todraw the material. For example, a fiber draw aspirator may be employed,such as a linear fiber aspirator of the type shown in U.S. Pat. Nos.3,802,817 and 3,423,255. A fiber draw aspirator generally includes anelongated vertical passage through which the fibers are drawn byaspirating air entering from the sides of the passage and flowingdownwardly through the passage. A heater or blower may supply theaspirating air, which causes the fibers to draw or attenuate.

Regardless of the particular technique employed, the polymeric matetypically drawn (e.g., in the machine direction) to a draw ratio of fromabout 1.1 to about 3.5, in some embodiments from about 1.2 to about 3.0,and in some embodiments, from about 1.3 to about 2.5. The draw ratio maybe determined by dividing the length of the drawn material by its lengthbefore drawing. The draw rate may also vary to help achieve the desiredproperties, such as within the range of from about 5% to about 1500% perminute of deformation, in some embodiments from about 20% to about 1000%per minute of deformation, and in some embodiments, from about 25% toabout 850% per minute of deformation.

Mechanical drawing in the manner described above can result in theformation of pores that have a “nano-scale” dimension (“nanopores”).such as an average cross-sectional dimension of about 800 nanometers orless, in some embodiments from about 5 to about 250 nanometers, and insome embodiments, from about 10 to about 100 nanometers. Micropores mayalso be formed at and around the micro-scale domains during drawing thathave an average cross-sectional dimension of from about 0.5 to about 30micrometers, in some embodiments from about 1 to about 20 micrometer andin some embodiments, from about 2 micrometers to about 15 micrometers.The micropores and/or nanopores may have any regular or irregular shape,such as spherical, elongated, etc. In certain cases, the axial dimensionof the micropores and/or nanopores may be larger than thecross-sectional dimension so that the aspect ratio (the ratio of theaxial dimension to the cross-sectional dimension) is from about 1 toabout 30, in some embodiments from about 1.1 to about 15, and in someembodiments, about 1.2 to about 5. The “axial limens on” is thedimension in the direction of the major axis (e.g., length), which istypically in the direction of drawing.

The present inventors have also discovered that the pores (e.g.,micropores, nanopores, or both) can be distributed in a substantiallyhomogeneous fashion throughout the material. For example, the pores maybe distributed in columns that are oriented in a direction generallyperpendicular to the direction in which a stress is applied. Thesecolumns may be generally parallel to each other across the width of thematerial. Without intending to be limited by theory believed that thepresence of such a homogeneously distributed porous network, can resultin a high thermal resistance as ell as good mechanical properties (e.g.,energy dissipation under load and impact strength). This is in starkcontrast to conventional techniques for creating pores that involve theuse of blowing agents, which tend to result in an uncontrolled poredistribution and poor mechanical properties. Notably the formation ofthe porous network by the process described above does not necessarilyresult in a substantial change in the cross-sectional size (e.g., width)of the material. In other words, the material is not substantiallynecked, which may allow the material to retain a greater degree ofstrength properties.

In addition to forming a porous network, mechanical drawing can alsosignificantly increase the axial dimension of the micro-scale domains sothat they have a generally linear, elongated shape. For example, theelongated micro-scale domains may have an average axial dimension thatis about 10% or more, in some embodiments from about 20% to about 500%,and in some embodiments, from about 50% to about 250% greater than theaxial dimension of the domains prior to drawing. The axial dimensionafter drawing may, for instance, range from about 0.5 to about 250micrometers, in some embodiments from about 1 to about 100 micrometers,in some embodiments from about 2 to about 50 micrometers, and in someembodiments, from about 5 to about 25 micrometers. The micro-scaledomains may also be relatively thin and thus have a smallcross-sectional dimension. For instance, the cross-sectional dimensionmay be from about 0.05 to about 50 micrometers, in some embodiments fromabout 0.2 to about 10 micrometers, and in some embodiments, from 0.5 toabout 5 micrometers. This may result in an aspect ratio for themicro-scale domains (the ratio of the axial dimension to thecross-sectional dimension) of from about 2 to about 150, in someembodiments from about 3 to about 100, and in some embodiments, fromabout 4 to about 50.

As a result of the porous and elongated domain structure, the presentinventors have discovered that the resulting polymeric material canexpand uniformly in volume when drawn in longitudinal direction, whichis reflected by a low “Poisson coefficient”, as determined according tothe following equation:

Poisson coefficient=−E _(transverse) /E _(longitudinal)

where E_(transverse) the transverse deformation of the material andE/_(longitudinal) is the longitudinal deformation of the material. Moreparticularly, the Poisson coefficient of the material can beapproximately 0 or even negative, For example, the Poisson coefficientmay be about 0.1 or less, in some embodiments about 0.08 or less, and insome embodiments, from about −0.1 to about 0.04. When the Poissoncoefficient is zero, there is no contraction in transverse directionwhen the material is expanded in the longitudinal direction. When thePoisson coefficient is negative the transverse or lateral dimensions ofthe material are also expanding when the material is drawn in thelongitudinal direction. Materials having a negative Poisson coefficientcoefficient can thus exhibit an increase in width when drawn in thelongitudinal direction, which can result in increased energy absorptionin the cross direction.

If desired, the polymeric material of the present invention may besubjected to one or more additional processing steps, before and/orafter being drawn. Examples of such processes include, for instance,groove roll drawing, embossing, coating, etc. In certain embodiments,the polymeric material may also be annealed to help ensure that itretains the desired shape. Annealing typically occurs at or above theglass transition temperature of the polymer matrix, such as at fromabout 40° to about 120° C., in some embodiments from about 50° C. toabout 100° C., and in some embodiments, from a bout 70° C. to about 90°C. The polymeric material may also be surface treated using any of avariety of known techniques to improve its properties. For example, highenergy beams (e.g., plasma, x-rays, e-beam, etc.) may be used to removeor reduce any skin layers, to change the surface polarity, porosity,topography, to embrittle a surface layer, etc. If desired, such surfacetreatment may be used before and/or drawing of the thermoplasticcomposition.

IV. Articles

The polymeric material of the present invention may generally have avariety of different depending on the particular application, such asfilms, fibrous materials, molded articles, profiles, etc., as well ascomposites and laminates thereof. In one embodiment, for example, thepolymeric material in the form of a film or layer of a film. Multilayerfilms may contain from two (2) to fifteen (15) layers, and in someembodiments, from three (3) to twelve (12) layers. Such multilayer filmsnormally contain at least one base layer and at least one additionallayer (e.g., skin layer), but may contain any number of layers desired.For example, the multilayer film may be formed from a base layer and oneor more skin layers wherein the base layer and/or skin layer(s) areformed from the polymeric material of the present invention. It shouldbe understood, however, that other polymer materials may also beemployed in the base layer and/or skin layer(s), such as polyolefinpolymers.

The thickness of the film may be relatively small to increaseflexibility. For example, the film may have a thickness of from about 1to about 200 micrometers, in some embodiments from about 2 to about 150micrometers, in some embodiments from about 5 to about 100 micrometers,and in some embodiments, from about 10 to about 60 micrometers. Despitehaving such a small thickness, the film may nevertheless be able toretain good mechanical properties during use. For example, the film maybe relatively ductile. One parameter that is indicative of the ductilityof the film is the percent elongation of the film at its break point, asdetermined by the stress strain curve, such as obtained in accordancewith ASTM Standard D638-10 at 23° C. For example, the percent elongationat break of the film in the machine direction (“MD”) may be about 10% ormore, in some embodiments about 50% or more, in some embodiments about80% a in some embodiments, from about 100% to about 600%. Likewise, thepercent elongation at break of the film in the cross-machine direction(“CD”) may be about 15% or more, in some embodiments about 40% or more,in some embodiments about 70% or more, and in some embodiments, fromabout 100% to about 400% Another parameter that is indicative ofductility is the tensile modulus of the film, which is equal to theratio of the tensile stress to the tensile strain and is determined fromthe slope of a stress-strain curve. For example, the film typicallyexhibits a MD and/or CD tensile modulus about 2500 Megapascals (“MPa”)or less, in some embodiments about 2200 MPa or less, in some embodimentsfrom about 50 MPa to about 2000 MPa, and in some embodiments, from about100 MPa to about 1000 MPa. The tensile modulus may be determined inaccordance with ASTM D638-10 at 23° C.

Although the film is ductile, it can still be relatively strong. Oneparameter that is indicative of the relative strength of the film is theultimate tensile strength, which is equal to the peak stress obtained ina stress-strain curve, such as obtained in accordance with ASTM StandardD638-10. For example, the film may exhibit an MD and/or CD peak stressof from about 5 to about 65 MPa, in some embodiments from about 10 MPato about 60 MPa, and in some embodiments, from about 20 MPa to about 55MPa. The film may also exhibit an MD and/or CD break stress of fromabout 5 MPa to about 60 MPa, in some embodiments from about 10 MPa toabout 50 MPa, and in some embodiments, from about 20 MPa to about 45MPa. The peak stress and break stress may be determined in accordancewith ASTM D638-10 at 23° C.

In addition to a film, the polymeric material may also be in the form ofa fibrous material or a layer or component of a fibrous material, whichcan include individual staple fibers or filaments (continuous fibers),as well as yarns, fabrics, etc. formed from such fibers. Yarns mayinclude, for instance, multiple staple fibers that are twisted together(“spun yarn”), filaments laid together without twist (“zero-twistyarn”), filaments laid together with a degree of twist, single filamentwith or without twist (“monofilament”), etc. The yarn may or may not betexturized. Suitable fabrics may likewise include, for instance, wovenfabrics, knit fabrics, nonwoven fabrics (e.g., spunbond webs, meltblownwebs, bonded carded webs, wet-laid webs, airlaid webs, coform webs,hydraulically entangled webs, etc.), and so forth.

Fibers formed from the thermoplastic composition may generally have anydesired configuration, including monocomponent and multicomponent (e.g.,sheath-core configuration, side-by-side configuration, segmented pieconfiguration, island-in-the-sea configuration, and so forth). In someembodiments, the fibers may contain one or more additional polymers as acomponent (e.g., bicomponent) or constituent (e.g., biconstituent) tofurther enhance strength and other mechanical properties. For instance,the thermoplastic composition may form sheath component of a sheath/corebicomponent fiber, while an additional polymer may form the corecomponent, or vice versa. The additional polymer may be a thermoplasticpolymer such as polyesters, e.g., polylactic acid, polyethyleneterephthalate, polybutylene terephthalate, and so forth; polyolefins,e.g., polyethylene, polypropylene, polybutylene, and so forth;polytetrafluoroethylene; polyvinyl acetate; polyvinyl chloride acetate;polyvinyl butyral; acrylic resins, e.g., polyacrylate,polymethylacrylate, polymethylmethacrylate, and so forth; polyamides,e.g., nylon; polyvinyl chloride; polyvinylidene chloride; polystyrene;polyvinyl alcohol; and polyurethanes.

When employed, the fibers can deform upon the application of strain,rather than fracture. The fibers may thus continue to function as, aload bearing member even after the fiber has exhibited substantialelongation. In this regard, the fibers of the present invention arecapable of exhibiting improved “peak elongation properties, i.e., thepercent elongation of the fiber at its peak load. For example, thefibers of the present invention may exhibit a peak elongation of about50% or more, in some embodiments about 100% or more, in some embodimentsfrom about 200% to about 1500%, and in some embodiments, from about 400%to about 800%, such as determined in accordance with ASTM D638-10 at 23°C. Such elongations may be achieved for fibers having a wide variety ofaverage diameters such as those ranging from about 0.1 to about 50micrometers, in some embodiments from about 1 to about 40 micrometers,in some embodiments from about 2 to about 25 micrometers, and in someembodiments, from about 5 to about 15 micrometers.

While possessing the ability to extend under strain, the fibers of thepresent invention can also remain relatively strong. For example, thefibers may exhibit a peak tensile stress of from about 25 to about 500Megapascals (“MPa”), in some embodiments from about 50 to about 300 MPaand in some embodiments from about 60 to about 200 MPa, such asdetermined in accordance with ASTM D638-10 at 23° C. Another parameterthat is indicative of the relative strength of the fibers of the presentinvention is “tenacity”, which indicates the tensile strength of a fiberexpressed as force per unit linear density. For example, the fibers ofthe present invention may have a tenacity of from about 0.75 to about6.0 grams-force (“g_(f)”) per denier in some embodiments from about 1.0to about 4.5 g_(f) per denier, and in some embodiments, from about 1.5to about 4.0 g_(f) per denier. The denier of the fibers may varydepending on the desired application. Typically, the fibers are formedto have a denier per filament (i.e., the unit of linear density equal tothe mass in grams per 9000 meters of fiber) of less than about 6, insome embodiments less than about 3, and in some embodiments, from about0.5 about 3.

Due to its unique and beneficial properties the resulting polymericmaterial of the present invention is well suited for use in a variety ofdifferent types of articles, such as an absorbent article, packagingfilm, barrier film, medical product (e.g., gown, surgical drape,facemask head covering, surgical cap, shoe covering, sterilization wrap,warming blanket, heating pad, etc.), and so forth. For example, thepolymeric material may be incorporated into an “absorbent article” thatis capable of absorbing water or other fluids. Examples of someabsorbent articles include, but are not limited to, personal careabsorbent articles, such as diapers training pants, absorbentunderpants, incontinence articles, feminine hygiene products (e.g.,sanitary napkins) swim wear, baby wipes, mitt wipe, and so forth;medical absorbent articles, such as garments, fenestration materials,underpads, bedpads, bandages, absorbent drapes, and medical wipes; foodservice wipers; clothing articles; pouches, and so forth. Materials andprocesses suitable for forming such articles are well known to thoseskilled in the art. Absorbent articles, for instance, typically includea substantially liquid-impermeable layer (e.g., outer cover), aliquid-permeable layer (e.g., bodyside liner, surge layer, etc.), and anabsorbent core. In one embodiment, for example, the polymeric materialmay be in the form of a fibrous <material (e.g., nonwoven web) and usedto form an outer cover of an absorbent article. If desired, the nonwovenweb may be laminated to a liquid-impermeable film that is eithervapor-permeable or vapor-impermeable. The polymeric material maylikewise be in the form of a film that is used in an absorbent article,such as a liquid-impermeable film of the outer cover, which is eithervapor-permeable or vapor-impermeable.

The polymeric material may also be employed in a wide variety of othertypes of articles. Non-limiting examples include, for instance,insulation materials for refrigeration units (e.g., refrigerators,freezers, vending machines, etc.); automotive components (e.g., frontand rear seats, headrests, armrests, door panels, rear shelves/packagetrays, steering wheels and interior trim, dashboards, etc.); buildingpanels and sections (e.g., roofs, wall cavities, under floors, etc.);apparel (e.g., coats, shirts, pants, gloves, aprons, coveralls, shoes,boots, headware, sock liners, etc.); furniture and bedding (e.g.,sleeping bags, comforters, etc.); fluid storage/transfer systems (e.g.,pipes or tankers for liquid/gas hydrocarbons, liquid nitrogen, oxygen,hydrogen, or crude oil); extreme environments (e.g., underwater orspace); food and beverage products (e.g., cups, cup holders platesetc.); containers and bottles; and so forth. The polymeric material mayalso be used in a “garment”, which is generally meant to include anyarticle that is shaped to fit over a portion of a body, Examples of sucharticles include, without limitation, clothing (e.g., shirts, pantsjeans, slacks, skirts, coats, activewear, athletic, aerobic, andexercise apparel, swimwear, cycling jerseys or shorts, swimsuit/bathingsuit, race suit, wetsuit, bodysuit, etc.), footwear (e.g., shoes, socks,boots, etc.), protective apparel (e.g., firefighter's coat), clothingaccessories (e.g., belts, bra straps, side panels, gloves, hosiery,leggings, orthopedic braces, etc.), undergarments (e.g., underweart-shirts, etc.), compression garments, draped garments (e.g., kiltsloincloths, togas, ponchos, cloaks, shawls, etc.), and so forth.

The polymeric material may be employed in a wide variety of articleswithin any particular application. For example, when consideringautomotive applications, the polymeric material may be employed infibrous articles or as solid moldings. By way of example, fibers of thepolymeric material may be beneficially employed in articles that canenhance comfort and/or aesthetics of a vehicle (e.g., coverings and/orpaddings for sun visors, speaker housings and coverings, seat coverings,seat slip agents, and backings for seat coverings, carpeting and carpetreinforcement including carpet backing, car mats and backings for carmats coverings for seat belts and seat belt anchorages, trunk floorcoverings and liners, rear shelf panels, headliner facings and backings,upholstery backings, general decorative fabrics, etc.), materials thatcan provide general temperature and/or noise insulation (e.g., columnpadding, door trim pads, hood liners general sound proofing andinsulation materials, muffler wraps, bodywork parts, windows, saloonroofs and sunroofs, tire reinforcements, etc.), and filtration/enginematerials (e.g., fuel filters, oil filters, battery separators, cabinair filters, transmission tunnel materials, fuel tanks, etc.).

Solid moldings including the polymeric material can be utilized toenhance automotive safety components For instance, the polymericmaterial can be encompassed in passive safety components such as crumplezones on the rear, front, and/or sides of a vehicle; within the safetycell of the automobile as a component of the airbag or steering wheel(e.g., collapsible steering column); as a cargo barrier; or as acomponent of a pedestrian safety system (e.g., as a component of thebumpers, hood, window frame etc.).

The low density of the polymeric material can provide weight savingbenefits in automotive applications. For example, the polymeric materialcan be a component of the structure of an automobile including, withoutlimitation, the hood, bumpers and/or bumper supports, the trunk lidand/or compartment, and the underbody of the vehicle.

Such broad-based application of the polymeric material is applicable toa wide variety of fields, and is not intended to be in any way limitedto the automotive industry. For instance, the polymeric material can beused in the transportation industry in any suitable applicationincluding, without limitation, air and space applications (e.g.,airplanes, helicopters, space transports, military aerospace devices,etc.), marine applications (boats, ships, recreational vehicles),trains, and so forth. The polymeric material can be utilized intransportation applications in any desired fashion, e.g., in fibrousarticles or solid moldings, in aesthetic applications, for temperatureand/or noise insulation in filtration and/or engine components, insafety components, etc.

The present invention may be better understood With reference to thefollowing examples.

TEST METHODS Conductive Properties:

Thermal conductivity (W/mK) and thermal resistance (m²K/W) weredetermined in accordance with ASTM E-1530-11 (“Resistance to ThermalTransmission of Materials by, the Guarded Heat Flow Meter Technique”)using an Anter Unitherm Model 2022 tester. The target test temperaturewas 25° C. and the applied load was 0.17 MPa. Prior to testing, thesamples were condition for 40+ hours at a temperature of 23° C. (+2° C.)and relative humidity of 50% (±10%). Thermal admittance (W/m²K) was alsocalculated by dividing 1 by the thermal resistance.

Melt Flow Rate:

The melt flow rate (“MFR”) is the weight of a polymer (in grams) forcedthrough an extrusion rheometer orifice (0.0825-inch diameter) whensubjected to a load of 2160 grams in 10 minutes, typically at 190° C.,210° C. or 230° C. Unless otherwise indicated, melt flow rate ismeasured in accordance with ASTM Test Method D1239 with a Tinius OlsenExtrusion Plastometer.

Thermal Properties:

The glass transition temperature (T_(g)) may be determined by dynamicmechanical analysis (DMA) in accordance with ASTM E1640-09. A Q800instrument from TA Instruments may be used. The experimental runs may beexecuted in tension/tension geometry, in a temperature sweep mode in therange from −120° C. to 150° C. with a heating rate of 3° C./min. Thestrain amplitude frequency may be kept constant (2 Hz) during the test.Three (3) independent samples may be tested to get an average glasstransition temperature, which is defined by the peak value of the tan δcurve, wherein tan δ is defined as the ratio of the loss modulus to thestorage modulus (tan δ=E″/E′).

The melting temperature may be determined by differential scanningcalorimetry (DSC). The differential scanning calorimeter may be a DSCQ100 Differential Scanning calorimeter, which may be outfitted with aliquid nitrogen cooling accessory and with a UNIVERSAL ANALYSIS 2000(version 4.6.6) analysis software program, both of which are availablefrom T.A. Instruments In of New Castle, Del. To avoid directly handlingthe samples, tweezers or other tools may be used. The samples may beplaced into an aluminum pan and weighed to an accuracy of 0.01 milligramon an analytical balance A lid may be crimped over the material sampleonto the pan. Typically, the resin pellets may be placed directly in theweighing pan.

The differential scanning calorimeter may be calibrated using an indiumMetal standard and a baseline correction may be performed, as describedin the operating manual for the differential scanning calorimeter. Amaterial sample may be placed into the test chamber of the differentialscanning calorimeter for testing and an empty pan may be used as areference. All testing may be run with a 55-cubic centimeter per minutenitrogen (industrial grade) purge on the test chamber. For resin pelletsamples the heating and cooling program is a 2-cycle test that beganwith an equilibration of the chamber to −30° C., followed by a firstheating period at a heating rate of 10° C. per minute to a temperatureof 200° C. followed by equilibration of the sample at 200° C. for 3minutes, followed by a first cooling period at a cooling rate of 10° C.per minute to a temperature of −30° C., followed by equilibration of thesample at −30° C. for 3 minutes, and then a second heating period at aheating rate of 10° C. per minute to a temperature of 200° C. For fibersamples, the heating and cooling program may be a 1-cycle test thatbegins with an equilibration of the chamber to −25° C., followed by aheating period at a heating rate of 10° C. per minute to a temperatureof 200° C., followed by equilibration of the sample at 200° C. for 3minutes, and then a cooling period at a cooling rate of 10° C. perminute to a temperature of −30° C. All testing may be run with a55-cubic centimeter per minute nitrogen (industrial grade) purge on thetest chamber.

The results may be evaluated using the UNIVERSAL ANALYSIS 2000 analysissoftware program, which identifies and quantifies the glass transitiontemperature (T_(g)) of inflection, the endothermic and exothermic peaks,and the areas under the peaks on the DSC plot. The glass transitiontemperature may be identified as the region on the plot-line where adistinct change in slope occurred, and the melting temperature may bedetermined using an automatic inflection calculation,

Film Tensile Properties:

Films may be tested for tensile properties (peak stress, modulus, strainat break, and energy per volume at break) on a MTS Synergie 200 tensileframe. The test may be performed in accordance with ASTM D638-10 (atabout 23° C.). Film samples may be cut into dog bone shapes with acenter width of 3.0 mm before testing. The dog-bone film samples may beheld in place using grips on the MTS Synergie 200 device with a gaugelength of 18.0 mm. The film samples may be stretched at a cross headspeed of 5.0 in/min until breakage occurred. Five samples may be testedfor each film in both the machine direction (MD) and the cross direction(CD). A computer program (e.g., TestWorks 4) may be used to collect dataduring testing and to generate a stress versus strain curve from which anumber of properties may be determined, including modulus, peak stress.elongation, and energy to break.

Fiber Tensile Properties:

Fiber tensile properties may be determined in accordance with ASTM638-10 at 23° C. For instance, individual fiber specimens may initiallybe shortened (e.g., cut with scissors) to 38 millimeters in length, andplaced separately on a black velvet cloth. 10 to 15 fiber specimens maybe collected in this manner. The fiber specimens may then be mounted ina substantially straight condition on a rectangular paper frame havingexternal dimension of 51 millimeters×51 millimeters and internaldimension of 25 millimeters×25 millimeters. The ends of each fiberspecimen may be operatively attached to the frame by carefully securingthe fiber ends to the sides of the frame with adhesive tape Each fiberspecimen may be measured for its external, relatively shorter,cross-fiber dimension employing a conventional laboratory microscope,which may be properly calibrated and set at 40× magnification. Thiscross-fiber dimension may be recorded as the diameter of the individualfiber specimen. The frame helps to mount the ends of the sample fiberspecimens in the upper and lower grips of a constant rate of extensiontype tensile tester in a manner that avoids excessive damage to thefiber specimens

A constant rate of extension type of tensile tester and an appropriateload cell may be employed for the testing. The load cell may be chosen(e.g., 10N) so that the test value falls within 10-90% of the full scaleload. The tensile tester (i.e., MTS SYNERGY 200) and load cell may beobtained from MTS Systems Corporation of Eden Prairie, Mich. The fiberspecimens in the frame assembly may then be mounted between the grips ofthe tensile tester such that the ends of the fibers may be operativelyheld by the grips of the tensile tester. Then, the sides of the paperframe that extend parallel to the fiber length may be cut or otherwiseseparated so that the tensile tester applies the test force only to thefibers. The fibers may be subjected to a pull test at a pull rate andgrip speed of 12 inches per minute. The resulting data may be analyzedusing a TESTWORKS 4 software program from the MTS Corporation with thefollowing test settings:

Calculation Inputs Test Inputs Break mark drop   50% Break sensitivity90% Break marker 0.1 in Break threshold 10 gr elongation Nominal gagelength 1 in Data Acq. Rate 10 Hz Slack pre-load 1 lb_(f) Danier length9000 m Slope segment length   20% Density 1.25 g/cm³ Yield offset 0.20%Initial speed 12 in/min Yield segment length   2% Secondary speed 2in/min

The tenacity values may be expressed in terms of gram-force per denier.Peak elongation (% strain at break) and peak stress may also bemeasured.

Expansion Ratio, Density, and Percent Pore Volume:

To determine expansion ratio, density, and percent pore volume, thewidth (W_(i)) and thickness (T_(i)) of the specimen may be initiallymeasured prior to drawing. The length (L_(i)) before drawing may also bedetermined by measuring the distance between two markings on a surfaceof the specimen. Thereafter, the specimen may be drawn to initiatevoiding. The width (W_(f)), thickness (T_(f)), and length (L_(f)) of thespecimen may then be measured to the nearest 0.01 mm utilizing DigimaticCaliper (Mitutoyo Corporation). The volume (V_(i)) before drawing may becalculated by W_(i)×T_(i)×L_(i)=V_(i). The volume (V_(f)) after drawingmay also be calculated by W_(f)×T_(f)×L_(f)=V_(f). The expansion ratio(Φ) may be calculated by (Φ=V_(f)/V_(i); the density (P_(f)) of wascalculated by: P_(f)=P_(i)/Φ, where P_(i) is density of precursormaterial, and the percent pare volume (% V_(v)) may be calculated by: %V_(v)=(1−1/Φ)×100.

Moisture Content:

Moisture content may be determined using an Arizona InstrumentsComputrac Vapor Pro moisture analyzer (Model No. 3100) in substantialaccordance with ASTM D 7191-05, which is incorporated herein in itsentirety by reference thereto for all purposes. The test temperature(§X2.1.2) may be 130° C., the sample size (§X2.1.1) may be 2 to 4 grams,and the vial purge time (§X2.1.4) may be 30 seconds. Further, the end incriteria (X2.1.3) may be defined as a “prediction” mode which means thatthe test is ended when the built-in program med criteria (whichmathematically calculates the end point moisture content) is satisfied.

EXAMPLE 1

The ability to initiate the formation of pores in a polymeric materialwas demonstrated. Initially a blend of 85.3 wt. % polylactic acid (PLA6201D, Natureworks®), 9.5 wt. % of a microinclusion additive, 1.4 wt. %of a nanoinclusion additive, and 3.8 wt. % of an interfacial modifierwas demonstrated. The microinclusion additive was Vistamaxx™ 2120(ExxonMobil), which is a polyolefin copolymer/elastomer with a melt flowrate of 29 g/10 min (190° C., 2160 g) and a density of 0.866 g/cm³. Thenanoinclusion additive was polyethylene-co-methyl acrylate-co-glycidylmethacrylate) (Lotader® AX8900, Arkema) having a melt flow rate of 5-6g/10 min (190° C./2160 g), a glycidyl methacrylate content of 7 to 11methyl acrylate content of 13 to 17 wt. %, and ethylene content of 72 to80 the internal interfacial modifier was PLURIOL® WI 285 Lubricant fromBASF which is a Polyalkylene Glycol Functional Fluids. The polymers werefed into a co-rotating, twin-screw extruder (ZSK-30, diameter of 30 mm,length of 1328 millimeters) for compounding that was manufactured byWerner and Pfleiderer Corporation of Ramsey, N.J. The extruder possessed14 zones, numbered consecutively 1-14 from the feed hopper to the die.The first barrel zone #1 received the resins via gravimetric feeder at atotal throughput of 15 pounds per hour. The PLURIOL® WI285 was added viainjector purr p into barrel zone #2. The die used to extrude the resinhad 3 die openings (6 millimeters in diameter) that were separated by 4millimeter. Upon formation, the extruded resin was cooled on afan-cooled conveyor belt and formed into pellets by a Conair pelletizer.The extruder screw speed was 200 revolutions per minute (“rpm”). Thepellets were then flood fed into a signal screw extruder heated to atemperature of 212° C. where the molten blend exited through 4.5 inchwidth slit die and drawn to a film thickness ranging from 0.54 to 0.58mm.

EXAMPLE 2

The sheet produced in Example 1 was cut to a 6″ length and then drawn to100% elongation using a MTS 820 hydraulic tensile frame in tensile modeat 50 mm/min.

EXAMPLE 3

The sheet produced in Example 1 was cut to a 6″ length and then drawn to150% elongation using a MTS 820 hydraulic tensile frame in tensile modeat 50 mm/min.

EXAMPLE 4

The sheet produced in Example 1 was cut to a 6″ length and then drawn to200% elongation using a MTS 820 hydraulic tensile frame in tensile modeat 50 mm/min.

The thermal properties of Examples 1-4 were then determined. The resultsare set forth in the table below.

Upper Lower Heat Mean Sample Surface Surface Sink Sample Thermal ThermalThermal Thickness Temp. Temp Temp Temp Resistance AdmittanceConductivity Example (mm) (° C.) (° C.) (° C.) (° C.) (m²K/W) (W/m²K)(W/mK) 1 0.58 40.5 30.0 11.3 35.3 0.0032 312.5 0.180 2 0.54 40.5 26.410.3 33.5 0.0054 185.2 0.100 3 0.57 40.5 26.1 10.3 33.3 0.0057 175.40.100 4 0.56 40.5 25.1 10.0 32.8 0.0064 156.3 0.087

EXAMPLE 5

Pellets were formed as described in Example 1 and then flood fed into aRheomix 252 single screw extruder with a L/D ratio of 25:1 and heated toa temperature of 212° C. where the molten blend exited through a Haake 6inch width s cast film the and drawn to a film thickness ranging from39.4 μm to 50.8 μm via Haake take-up roll. The film was drawn in themachine direction to a longitudinal deformation of 160% at a pull rateof 50 mm/min (deformation rate of 67%/min) via MTS Synergie 200 tensileframe with grips at a gage length of 75 mm.

EXAMPLE 6

Films were formed as described in Example 5 except that the film wasalso stretched in the cross-machine direction to a deformation of 100%at a pull rate of 50 mm/min (deformation rate of 100%/min) with grips ata gage length of 50 mm.

Various properties of the films of Examples 5-6 were tested as describedabove. The results are set forth below in Tables 1-2.

TABLE 1 Film Properties Average Thickness Expansion Ratio Percent VoidDensity Ex. (μm) (φ) Volume (% V_(v)) (g/cm³) 5 41.4 1.82 45 0.65 6 34.02.13 53 0.56

TABLE 2 Tensile Properties Avg. Avg. Avg. Yield Avg. Break Avg. StrainAvg. Energy per Thickness Modulus Stress Stress at Break Volume at BreakExample (μm) (MPa) (MPa) (MPa) (%) (J/cm³) 5 MD 44.5 466 41.4 36.9 54.616.8 CD 40.4 501 15.9 15.9 62.6 9.4 6 MD 37.3 265 26.7 26.3 85.5 15.8 CD34.3 386 25.1 25.2 45.8 9.3

EXAMPLE 7

Pellets were formed as described in Example 1 and then flood fed into asignal screw extruder heated to a temperature of 212° C., where themolten blend exited through 4.5 inch width slit die and drawn to a filmthickness ranging from 36 μm to 54 μm. The films were stretched in themachine direction to about 100% to initiate cavitation and voidformation. The morphology of the films was analyzed by scanning electronmicroscopy (SEM) before and after stretching. The results are shown inFIGS. 3-6. As shown in FIGS. 3-4, the microinclusion additive wasinitially dispersed in domains having an axial size On machinedirection) of from about 2 to about 30 micrometers and a transversedimension (in cross-machine direction) of from about 1 to about 3micrometers, while the nanoinclusion additive was initially dispersed asspherical or spheroidal domains having an axial size of from about 100to about 300 nanometers. FIGS. 5-6 show the film after stretching. Asindicated, pores formed around the microinclusion and nanoinclusionadditives. The micropores formed around the microinclusion additivegenerally had an elongated or slit-like shape with a broad sizedistribution ranging from about 2 to about 20 micrometers in the axialdirection The nanopores associated with the nanoinclusion additivegenerally had a size of from about 50 to about 500 nanometers.

EXAMPLE 8

The compounded pellets of Example 7 were dry blended with anothernanoinclusion additive, which was a halloisite clay masterbatch(MacroComp MNH-731-36 MacroM) containing 22 wt. % of a styreniccopolymer modified nanoclay and 78 wt. % polypropylene (Exxon Mobil3155). The mixing ratio was 90 wt. % of the pellets and 10 wt. % of theclay masterbatch, which provided a total clay content of 2.2%. The dryblend was then flood fed into a signal screw extruder heated to atemperature of 212° C., where the molten blend exited through 4.5 inchwidth slit die and drawn to a film thickness ranging from 51 to 58 μm.The films were stretched in the machine direction to about 100% toinitiate cavitation and void formation.

The morphology of the films as analyzed by scanning electron microscopy(SEM) before and after stretching. The results are shown in FIGS. 7-10.As shown in FIGS. 7-8, some of the nanoclay particles (visible asbrighter regions) became dispersed in the form of very smalldomains—i.e., axial dimension ranging from about 50 to about 300nanometers. The masterbatch itself also formed domains of a micro-scalesize (axial dimension of from about 1 to about 5 micrometers). Also, themicroinclusion additive (Vistamax™) formed elongated domains, while thenanoinclusion additives (Lotader®, visible as ultrafine dark dots andnanoclay masterbatch, visible as bright platelets) formed spheroidaldomains. The stretched film is shown in FIGS. 9-10. As shown, the voidedstructure is more open and demonstrates a broad variety of pore sizes.In addition to highly elongated micropores formed by the microinclusions(Vistamaxx™), the nanoclay masterbatch inclusions formed more openspheroidal micropores with an axial size of about 10 microns or less anda transverse size of about 2 microns. Spherical nanopores are alsoformed by the nanoinclusion additives (Lotader® and nanoclay particles).

Various tensile properties (machine direction) of the film Example 1 and2 were also tested. The results are provided below in Table 3.

TABLE 3 Avg. Avg. Avg. Yield Avg. Break Avg. Strain Avg. EnergyThickness Modulus Stress Stress at Break per Vol. Example (μm) (MPa)(MPa) (MPa) (%) (J/cm³) 1 49 2066 48.1 35 236 73 2 56 1945 41.3 36 29985

As shown, the addition of the nanoclay filler resulted in a slightincrease in break stress and a significant increase in elongation atbreak.

EXAMPLE 9

The ability to initiate the formation of pores in a polymeric materialwas demonstrated. Initially, a precursor blend was formed from 91.8 wt.% isotactic propylene homopolymer (M3661, melt flow rate of 14 g/10 at210° C. and melting temperature of 150° C., Total Petrochemicals), 7.4wt. % polylactic acid (PLA 6252, melt flow rate of 70 to 85 g/10 min at210° C. Natureworks®) and 0.7 wt. % of a polyepoxide. The polyepoxidewas poly(ethylene-co-methyacrylate-co-glycidyl methacrylate) (LOTADER®AX8900, Arkema) having a melt flow rate of 6 g/10 min (190° C./2160 g),a glycidyl methacrylate content of 8 wt. %, methyl acrylate content of24 wt. %, and ethylene content of 68 wt. %. The components werecompounded in a co-rotating twin-screw extruder (Werner and PfleidererZSK-30 with a diameter of 30 and a L/D=44), The extruder had sevenheating zones. The temperature in the extruder ranged from 180° C. to220° C. The polymer was fed gravimetrically to the extruder at the hoperat 15 pounds per hour and the liquid was injected into the barrel usinga peristaltic pump. The extruder was operated at 200 revolutions perminute (RPM). In the last section of the barrel (front), a 3-hole die of6 mm in diameter was used to form the extrudate. The extrudate was aircooled in a conveyor belt and pelletized using a Conair Pelletizer.

Fiber was then produced from the precursor blend using a Davis-Standardfiber spinning line equipped with a 0.75-inch single screw extruder and16 hole spinneret with a diameter of 0.6 mm. The fibers were collectedat different draw down ratios. The take up speed ranged from 1 to 1000m/min. The temperature of the extruder ranged from 175° C. to 220° C.The fibers were etched in a tensile tester machine at 300 mm/min up to400% elongation at 25° C. To analyze the material morphology, the fiberswere freeze fractured in liquid nitrogen and analyzed via ScanningElectron Microscope Jeol 6490LV at high vacuum. The results are shown inFIG. 11-13. As shown, spheroidal pores are formed that are elongated inthe stretching direction. Both nanopores (˜50 nanometers in width, ˜500nanometers n length) and micropores (˜0.5 micrometers in width, ˜4micrometers in length) were formed.

EXAMPLE 10

Pellets were formed as described in Example 1 and then flood fed into asingle screw extruder at 240° C., melted, and passed through a melt pumpat a rate of 0.40 grams per hole per minute through a 0.6 mm diameterspinneret. Fibers were collected in free fall (gravity only as drawforce) and then tested for mechanical properties at a pull rate of 50millimeters per minute. Fibers were then cold drawn at 23° C. in a MTSSynergie Tensile frame at a rate of 50 mm/min. Fibers were drawn topre-defined strains of 50%, 100%, 150%, 200% and 250%. After drawing,the expansion ratio, void volume and density were calculated for variousstrain rates as shown in the tables below.

Initial Initial Initial Length after Diameter after Volume after LengthDiameter Volume Strain elongation elongation elongation (mm) (mm)(mm{circumflex over ( )}3) % (mm) (mm) (mm{circumflex over ( )}3) 500.1784 1.2498 50.0 75 0.1811 1.9319 50 0.2047 1.6455 100.0 100 0.20513.3039 50 0.1691 1.1229 150.0 125 0.165 2.6728 50 0.242 2.2998 200.0 1500.1448 2.4701 50 0.1795 1.2653 250.0 175 0.1062 1.5502 Void InitialVoided Strain Poisson's Expansion Volume Density Density % CoefficientRatio (%) (g/cc) (g/cc) Observation 50 −0.030 1.55 35.3 1.2 0.78 Nonecking 100 −0.002 2.01 50.2 1.2 0.60 No necking 125 0.016 2.38 58.0 1.20.50 No necking 150 0.201 1.07 6.9 1.2 1.12 necking 175 0.163 1.23 18.41.2 0.98 fully necked

EXAMPLE 11

Fibers were formed as described in Example 10, except that they werecollected at a collection roll speed of 100 meters per minute resultingin a drawn down ratio of 77. Fibers were then tested for mechanicalproperties at a pull rate of 50 millimeters per minute. Fibers were thencold drawn at 23° C. in a MTS Synergie Tensile frame at a rate of 50mm/min. Fibers were drawn to pre-defined strains of 50%, 100%, 150%,200% and 250%. After drawing, the expansion ratio, void volume anddensity were calculated for various strain rates as shown in the tablesbelow.

Initial Initial Initial Length after Diameter after Volume after LengthDiameter Volume Strain elongation elongation elongation (mm) (mm)(mm{circumflex over ( )}3) % (mm) (mm) (mm{circumflex over ( )}3) 500.057 0.1276 50.0 75 0.0575 0.1948 50 0.0601 0.1418 100.0 100 0.06090.2913 50 0.067 0.1763 150.0 125 0.0653 0.4186 50 0.0601 0.1418 200.0150 0.058 0.3963 50 0.0601 0.1418 200.0 150 0.0363 0.1552 50 0.0590.1367 250.0 175 0.0385 0.2037 Void Initial Voided Strain Poisson'sExpansion Volume Density Density % Coefficient Ratio (%) (g/cc) (g/cc)Observation 50 −0.018 1.53 34.5 1.2 0.79 1 small neck ~1 mm in length100 −0.013 2.05 51.3 1.2 0.58 2 small necks approximately 5 mm in length150 0.017 2.37 57.9 1.2 0.51 No visible necking - fiber looks to beuniform 200 0.017 2.79 64.2 1.2 0.43 Average diameter taken from neckedand unnecked regions 200 0.198 1.09 8.6 1.2 1.10 Diameter only takenfrom necked region 250 0.139 1.49 32.9 1.2 0.81 Fully necked

EXAMPLE 12

Fibers were formed as described in Example 10, except that the blend wascomposed of 83.7 wt. % polylactic acid (PLA 6201D, Natureworks®), 9.3wt. % of Vistamaxx™ 2120, 1.4 wt. % Lotader® AX8900, 3.7% wt. % PLURIOL®WI 285 and 1.9% hydrophilic surfactant (Masil SF-19). The PLURIOL® WI285and Masil SF-19 were premixed at a 2:1 (WI-285:SF-19) ratio and addedvia injector pump into barrel zone #2. Fibers were collected at 240° C.,0.40 ghm and under free fall.

EXAMPLE 13

Fibers were formed as described in Example 12, except that they werecollected at a collection roll speed of 100 meters per minute resultingin a drawn down ratio of 77. Fibers were then tested for mechanicalproperties at a pull rate of 50 millimeters per minute. Fibers were thencold drawn at 23° C. in a MTS Synergic Tensile frame at a rate of 50mm/min. Fibers were drawn to pre-defined strain of 100%. After drawing,the expansion ratio, void volume and density were calculated as shown inthe tables below.

Initial Initial Initial Length after Diameter after Volume after LengthDiameter Volume Strain elongation elongation elongation Example (mm)(mm) (mm{circumflex over ( )}3) % (mm) (mm) (mm{circumflex over ( )}3)14 50 0.0626 0.1539 100.0 100 0.0493 0.1909 Void Initial VoidedPoisson's Expansion Volume Density Density Example Coefficient Ratio (%)(g/cm³) (g/cm³) Observation 14 0.2125 1.24 19.4 1.2 0.97 Localizednecking throughout

EXAMPLE 14

Fibers from Example 12 were stretched in a MTS synergic Tensile frame ata rate of 50 millimeters per minute to 250% strain. This opened up thevoid structure and turned the fiber white. A one inch sample was thencut from the stressed, white area of the fiber. The new fiber was thentested as described above. The density was estimated to be 0.75 gramsper cubic centimeters and the pull rate for the tensile test was 305mm/min.

EXAMPLE 15

Fibers from Example 11 were heated in an oven at 90° C. for 30 minutesto anneal the fiber.

EXAMPLE 16

Fibers from Example 11 were heated in an oven at 90° C. for 5 minutes toanneal the fiber and induce crystallization.

The fibers of Examples 10-16 were then tested for mechanical propertiesat a pull rate of 50 millimeters per minute. The results are set forthin the table below.

Peak Peak Strain at Energy to Diameter Load Stress Break Break TenacityDensity Example (μm) (g_(f)) (MPa) (%) (J/cm{circumflex over ( )}3)(g/g) (g/cm³) Control PLA 207.8 217.06 62.8 3.8 0.8 0.57 1.25 Fibers 10184.6 126.65 47.3 484.5 154.0 0.44 1.20 11 62.2 22.57 73.1 464.1 205.10.69 1.20 12 128.5 70.32 53.2 635.3 216.0 0.50 1.20 13 59.1 16.17 57.8495.8 184.4 0.55 1.20 14 108.5 92.95 101.3 110.8 71.2 1.49 ~0.75 15 67.524.48 66.9 467.7 195.2 0.63 1.20 16 62.6 19.55 62.2 351.0 154.4 0.591.20

EXAMPLE 17

The ability to form films from a blend of 85.3 wt. % polylactic acid(PLA 6201D, Natureworks®), 9.5 wt. % of Vistamaxx™ 2120, and 1.4 wt. %Lotader® AX8900 Arkema), and PLURIOL® WI 285 was demonstrated. Thepolymers were fed into co-rotating, twin-screw extruder that possessed11 zones, numbered consecutively 1-11 from the feed hopper to the die.The first barrel zone #1 received the resins via gravimetric feeder at atotal throughput of 500 pounds per hour, The PLURIOL® W1285 was addedvia injector pump into barrel zone #3. The molten resin blend was thenextruded through a 24-hole die and underwater pelletized. The pelletswere then flood fed into a signal screw extruder heated to a temperatureof 205° C. where the molten blend exited through 36 inch width slit dieand drawn to a film thickness ranging from 36 μm to 54 μm. The film wasthen drawn through a machine direction orientation draw unit consistingof 7 sets of nip rolls through which the material was stretched. Thefilm was drawn from 1.3 to 2.2× to initiate and grow the porousstructure. The process details and resulting density reduction are setforth in the table below.

Draw Film Quench MDO Draw Roll Density Reduction Condition Temp (° F.)Temperature (° F.) (%) — 75 N/A  0% 1.36X 75 100 18% 1.56X 75 100 29%1.75X 75 100 39% 1.94X 75 100 40% 1.78X 55 100 34% 1.94X 55 100 41%1.94X 55 120 36% 2.17X 55 100 44%

EXAMPLE 18

The resin from Example 17 was melt spun at 230° C. through a spinneretconsisting of 675 holes with an orifice size of 0.35 millimeters at athroughput of 0.28 grams per hole per minute. Fibers were melt drawn ona godet roll at a speed of 111 meters per minute and wound on to abobbin. The bobbin containing the fiber was then drawn from the bobbinon a staple fiber line at a draw ratio ranging from 1.25× to 1.75× andcollected as drawn fibers as well as cut into ˜35 mm.

Draw Condition Density Reduction (%) 1  0% 1.25X 20% 1.5X 30% 1.75X 40%

EXAMPLE 19

Fibers were formed as in Example 18 except the fiber had a throughput of0.36 grams per hole per minute and fibers were drawn on the staple fiberline at 1.25× to 2×.

Draw Condition Density Reduction (%) 1  0% 1.25X  7% 1.5X 17% 1.75X 23%2.0X 35%

EXAMPLE 20

Fibers were formed as in Example 19 except the 1^(st) zone of the staplefiber line was heated from 25° C. to 90° C. and fibers were draw from1.25× to 1.75×

Draw Condition Density Reduction (%) 1  0% 1.25X  5% 1.5X 14% 1.75X 15%

EXAMPLE 21

Fibers were formed as in Example 18 except the fiber had a throughput of0.36 grams per hole per minute and fibers were melt drawn on a godetroll at a speed of 76 motors per minute. Fibers were then drawn on thestaple fiber line from and fibers were drawn on the staple fiber line at1.25× to 2.5×.

Draw Condition Density Reduction (%) 1  0% 1.25X 16% 1.5X 28% 1.75X 33%2.0X 44% 2.5X 55%

While the invention has been described in detail with respect to thespecific embodiments thereof, it will be appreciated that those skilledin the art, upon attaining an understand in of the foregoing, mayreadily conceive of alterations to, variations of, and equivalents tothese embodiments. Accordingly, the scope of the present inventionshould be assessed as that of the appended claims and any equivalentsthereto.

1-28. (canceled)
 29. A method for initiating the formation of pores in apolymeric material that contains a thermoplastic composition, thethermoplastic composition including a continuous phase in which amicroinclusion additive and nanoinclusion additive are dispersed in theform of discrete domains, the continuous phase including a matrixpolymer, the method comprising mechanically drawing the polymericmaterial in a solid state to form a porous network, wherein the porousnetwork includes a plurality of nanopores having an averagecross-sectional dimension of about 800 nanometers or less.
 30. Themethod of claim 29, wherein the polymeric material is drawn at atemperature of from about −50° C. to about 125° C.
 31. The method ofclaim 29, wherein the polymeric material is drawn at a temperature thatis at least about 10° C. below the glass transition temperature of thematrix polymer and/or the microinclusion additive.
 32. The method ofclaim 29, wherein the nanopores have an average cross-sectionaldimension of from about 5 to about 700 nanometers.
 33. The method ofclaim 29, wherein the total pore volume of the polymeric material isfrom about 15% to about 80%.
 34. The method of claim 29, wherein thenanopores constitute about 15 vol.. % or more of the total pore volumein the polymeric material.
 35. The method of claim 29, wherein thematerial is drawn by passing the material between a nip defined betweentwo rolls.
 36. The method of claim 35, wherein at least one of the rollsis rotatable.
 37. The method of claim 35, wherein at least one of therolls contains a pattern of raised embossing elements.
 38. The method ofclaim 35, wherein at least one of the rolls contains a plurality ofgrooves.
 39. The method of claim 29, wherein the material is passed overa series of rolls that progressively draw the material.
 40. The methodof claim 29, wherein the material is drawn through a converging die. 41.The method of claim 40, wherein the material is pultruded through theconverging die.
 42. The method of claim 29, wherein the material isdrawn through the use of a fluidic medium.
 43. The method of claim 29,wherein the material is drawn through the use of a brake assembly. 44.The method of claim 29, wherein the continuous phase constitutes fromabout 60 wt. % to about 99 wt. % of the thermoplastic composition, themicroinclusion additive constitutes from about 1 wt. % to about 30 wt. %of the composition based on the weight of the continuous phase, and thenanoinclusion additive constitutes from about 0.05 wt. % to about 20 wt.% of the composition based on the weight of the continuous phase. 45.The method of claim 29, wherein the matrix polymer includes a polyesteror polyolefin.
 46. The method of claim 29, wherein the microinclusionadditive includes a polyolefin.
 47. The method of claim 29, wherein thenanoinclusion additive includes a polyepoxide.
 48. The method of claim29, wherein the thermoplastic composition further comprises aninterphase modifier.
 49. The method of claim 29, wherein the porousnetwork further includes micropores having an average cross-sectionaldimension of from about 0.5 to about 30 micrometers.
 50. The method ofclaim 29, wherein the micro-scale domains have an averagecross-sectional dimension of from about 0.5 micrometer to about 250micrometers.